Mcat Biology 3

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parathyroid hormone

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raises plasma Ca2+ levels by stimulating its release from bone; also regulates osteoblasts

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calcitonin

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inhibits calcium release from bone, i.e. lowers plasma calcium levels

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what regulates osteoclast activity?

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osteoblasts

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thymosin

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a hormone that stimulates pre-T cells to mature; secreted by the thymus

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enzyme found in tears

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lysozyme, can digest the peptidoglycan of many bacterial cell walls

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MHC

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major histocompatibility complex

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MHC class I

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proteins found on the surface of all cells

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MCH class II

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only present on immune cells, i.e. macrophages, B cells, T cells

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epitope

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specific part of an antigen that binds to the antibody (on its variable region)

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cellular organelle responsible for secretory proteins

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rough endoplasmic reticulum

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neuron structure

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an elongated cell consisting of dendrites, a cell body, and an axon

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dendrites

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cytoplasmic extensions that receive information and transmit it toward the cell body

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soma

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or the cell body; contains the nucleus and controls the metabolic activity of the neuron

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axon hillock

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connects the cell body to the axon (nerve fiber), which is a long cellular process that transmits impulses away from the cell body

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myelin

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an insulating substance that ensheathes most mammalian axons, allowing axons to conduct impulses faster; it is produced by glial cells

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glial cells

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also called oligodendrocytes (central nervous system), or Schwann cells (in the peripheral nervous system); produce myelin

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nodes of Ranvier

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gaps between segments of myelin along the axon

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synaptic terminals

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also called synaptic boutons or knobs; swellings at the end of axons, from which neurotransmitters are released into the synapse

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synapse

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or synaptic cleft; the gap between the axon terminals of one cell and the dendrites of the next

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demyelination

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the destruction of myelin; multiple sclerosis causes demyelination of the brain and spinal cord, resulting in a variety of symptoms (weakness, lack of balance, vision problems, and incontinence)

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resting potential

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the potential difference between the extracellular space and the intracellular space when a neuron is at rest; usually around -70 mV (inside of neuron is more negative than out)

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internal charge of a neuron

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is negative; a result of selective ionic permeability of the neuronal cell membrane, and maintained by the Na+/K+ ATPase (or pump). Potassium is higher inside the cell, so it diffuses down its gradient; but the membrane is impermeable to Na+ (which has a higher concentration outside), thus a net negative charge from proteins is left inside the cell.

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Na+/K+ ATPase

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the pump restores ionic gradients (after the transmission of action potentials) by using ATP energy to transport 3Na+ out for every 2K+ transported in.

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threshold membrane potential

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usually around -50 mV; this is the minimum depolarization needed to initiate an action potential in a nerve cell

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voltage-gated ion channels

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ion channels in the nerve cell membrane that open in response to changes in voltage; in response to depolarization, the voltage-gated Na+ channel opens first, causing a rapid depolarization of that segment of cell; then the voltage-gated K+ channels open, repolarizing the cell, i.e. returning the cell to a more negative potential.

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hyperpolarization

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upon opening the voltage-gated K+channels, repolarization occurs in a neuron cell; if the neuron exceeds its resting potential, becoming even more negative inside than normal, it is called hyperpolarization.

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refractory period

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a period of time following an action potential in which it is very difficult or impossible to initiate another action potential.

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TTX

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tetrodotoxin (found in the puffer fish); blocks the voltage-gated Na+ channels, thereby blocking neuronal transmitssion, and can rapidly cause death.

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how is neuronal information coded?

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by frequency and number of action potentials, not size or duration of them; action potential is an all-or-none response

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local anesthetics

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blocks the voltage-gated Na+ channels; works wel on sensory neurons b/c these neurons have small axonal diameters with little or no myelin, making it easier to prevent action potential propagation.

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direction of information travel

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from dendrite to synaptic terminal; this is b/c synapses operate only in one direction, and because refractory periods make the backward travel of action potentials impposible

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speed of propagation of action potentials

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increased diamter of the axon, and increased myelination = faster propagation

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saltatory conduction

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process in which the action potential "jumps" from node to node (due to the myelin insulated segments of the axon)

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nerve gas

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causes rapid death by preventing the action of skeletal muscle, leading to respiratory arrest

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inhibition of acetylcholinesterase

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allows elevation of synaptic levels of acetylcholine; used to treat glaucoma, also used by nerve gases

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cocaine and the nervous system

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blocks neuronal uptake carriers, thus prolonging hte action of neurotransmitters in the synapse by preventing neurotransmitter re-entry into the nere terminal

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chemical synapses

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the nerve terminal contains thousands of membrane-bound vesices full of neurotransmitters (chemical messengers); when the action potential arrives at the nerve terminal and depolarizes it, the synaptic vesicles fuse with the presynaptic membrane and release neurotransmitter into the synapse via a calcium-dependent process of exocytosis.

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uptake carrier

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a protein (in the presynaptic nerve terminal) that takes back neurotransmitters that were released into the synapse

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acetylcholinesterase

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inactivates the neurotransmitter acetylcholine

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afferent neurons

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sensory neurons = neurons that carry information about the external or internal environment to the brain or spinal cord

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efferent neurons

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motor neurons = neurons that carry commands from the brain or spinal cord to various parts of the body

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interneurons

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participate only in local circuits; their cell bodies and nerve terminals are in the same location

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nerves

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bundles of axons covered with connective tissue

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sensory vs. motor nerve

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a nerve that carries only sensory fibers vs. motor fibers (if both present = mixed nerve)

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ganglia

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clusters of neuronal cell bodies in the periphery

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nuclei

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clusters of neuronal cell bodies in the central nervous system

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Lou Gehrig's disease

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amyotrophic lateral sclerosis (ALS) = affects only motor neurons; eventually patients affected with this disease lose all motor control

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central nervous system

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brain and spinal cord

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brain

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jelly-like mass of neurons; consists of gray matter and white matter; can be divided into the forebrain, midbrain, and hindbrain

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gray vs. white matter

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cell bodies vs. myelinated axons

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forebrain

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consists of the telencephalon and the diencephalon

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telencephalon

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two hemispheres, each of which can be divided into four lobes (frontal, parietal, temporal, and occipital); also includes the cerebral cortex

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cerebral cortex

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highly convoluted gray matter that can be seen on the surface of the brain; the cortex processes and integrates sensory input and motor responses and is important for memory and creative thought

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corpus callosum

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the path through which righ and left cerebral cortices communicate

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diencephalon

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contains the thalamus and hypothalamus

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thalamus

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a relay and integration center for the spinal cord and cerebral cortex

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hypothalamus

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controls visceral functions such as hunger, thirst, sex drive, water balance, blood pressure, and temperature regulation; also plays an important role in the control of the endocrine system

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midbrain

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relay center for visual and auditory impulses; also plays an important role in motor control

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hindbrain

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consists of the cerebellum, the pons, and the medulla

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cerebellum

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helps modulate motor impulses initated by the motor cortex, and is important in the maintenance of balance, hand-eye coordination, and the timing of rapid movements

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pons

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acts as a relay center to allow the cortex to communicate with the cerebellum

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medulla (oblongata)

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controls many vital functions such as breathing, heart rate, and gastrointestinal acitivty

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brainstem

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midbrain, pons, and medulla

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frontal lobe syndrome

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damage to the frontal lobe that results in a personality change; e.g. Phineas Gage became rude, obnoxious, and socially uninhibited

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spinal cord

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an elongated strucuture continuous with the brainstem, that extends down the dorsal side of vertebrates; can integrate simple motor responses (reflexes) by itself

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cross sectional structure of spinal cord

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outer white matter area containing motor and sensory axons and an inner gray matter area containing nerve cell bodies

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information path in the spinal cord

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sensory information enters dorsally (cell bodies of the sensory neurons are located in the dorsal root ganglia); and all motor information exits the spinal cord ventrally

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roots

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nerve branches entering and leaving the cord

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spinal cord regions

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cervical, thoracic, lumbar, and sacral

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peripheral nervous system

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consists of 12 pairs of cranial nerves (exit from the brainstem), which primarily innervate the head and shoulders; and 31 pairs of spinal nerves (exit from the spinal cord), which innervate the rest of the body; PNS has two primary divisions = somatic and autonomic nervous systems

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myasthenia gravis

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an autoimmune disorder in which the body mounts an immune response against the acetylcholine receptors on the skeletal muscle; symptoms include weakness and fatigue and the severity varies greatly.

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somatic nervous system

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innervates skeletal muscles and is responsible for voluntary movement, and reflex action.

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acetylcholine

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ACh -- a neurotransmitter released by motor neurons onto ACh receptors located on skeletal muscle; this causes depolarization of the skeletal muscle, leading to muscle contraction.

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monosynaptic reflexes

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these pathways have only one synapse between the sensory neuron and the motor neuron; e.g., knee-jerk reflex, stretch receptors in the tendon covering the patella sense the hit and send action potentials up the sensory neuron into the spinal cord. The sensory neuron synapses with a motor neuron in the spinal cord, which stimulates the quadriceps muscle to contract.

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polysynaptic reflexes

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sensory neurons synapse with more than one neuron; e.g., withdrawal reflex - when a person steps on a nail, the injured leg withdraws in pain, while the other leg extends to retain balance.

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reflexes

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occur at the level of the spinal cord and do not require the participation of the brain (usually a faster response)

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autonomic nervous system

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sometimes called the involuntary nervous system; innervates cardiac and smooth muscle; ANS pathways are characterized by a two-neuron system.

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two-neuron system of the ANS

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first neuron (preganglionic neuron) has a cell body located within the CNS and its axon synapses in peripheral ganglia; while the second neuron (postganglionic neuron) has its cell body in the ganglia and then synapses on cardiac or smooth muscle.

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subdivisions of the ANS

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sympathetic and parasympathetic nervous systems

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sympathetic nervous system

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responsible for "flight or fight" responses that ready the body for action = increase blood pressure, heart rate, blood flow to skeletal muscles, and decreases gut motility.

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preganglionic sympathetic neurons

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emerge from the thoracic and lumbar regions of the spinal cord and us ACh as the neurotransmitter; also cause the adrenal medulla to release adrenaline (epinephrine) into the bloodstream.

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postganglionic sympathetic neurons

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typically release norepinephrine

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parasympathetic nervous system

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acts to conserve energy and restore the body to resting acivity levels following exertion (rest and digest) = lowers heart rate, increases gut motility; neurons originate in the brainstem (cranial nerves) and the sacral part of the spinal cord; both preganglionic and postganglionic neurons release ACh.

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vagus nerve

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a parasympathetic nerve that innervates many of the thoracic and abdominal viscera

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length of axons in sympathetic NS vs. parasympathetic NS

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short preganglionic and long postganglionic axons vs. the opposite

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types of sensory receptors

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interoceptors, proprioceptors, and exteroceptors

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interoceptors

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monitor aspects of the internal environment, such as blood pressure, [CO2] in blood, and blood pH.

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proprioceptors

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transmit information regarding the position of the body in space; these receptors are located in muscles and tendons to tell the brain where the limbs are in space, and are also located in the inner ear to tell the brain where the head is in space.

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exteroceptors

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sense things in the external environment such as light, sound, taste, pain, touch and temperature

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sclera

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a thick, opaque layer that covers the eyeball. Also known as the white of the eye

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choroid layer

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beneath the sclera; this layer helps to supply the retina with blood

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retina

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the innermost layer of the eye, which contains the photoreceptors that transduce light into action potentials

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cornea

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transparent, at the front of the eye; bends and focuses light rays

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pupil

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an opening in the eye through which rays can travel; its diameter is controlled by the iris

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iris

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pigmented and muscular, the iris responds to the intensity of light in the surroundings, and contracts to change the diameter of the pupil.

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the lens of the eye

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suspended behind the pupil; the shape of the lens is controlled by the ciliary muscles, and focuses the image onto the retina; it is a convex (converging) lens, so it forms an inverted and reversed image on the focal plane (retina)

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types of photoreceptors in the eye

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cones and rods

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cones

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respond to high-intensity illumination and are sensitive to color; contain 3 different pigments that absorb red, green, and blue wavelengths

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rods

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detect low-intensity illumination and are important in night vision

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rhodopsin

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the rod pigment, which absorbs one wavelength

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presbyopia

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with age, the lens becomes less elastic and has more difficulty 'rounding up,' something that needs to occur for near vision. So people become more far-sighted as they age.

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information from the photoreceptor cells travel...

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photoreceptor cells synapse onto bipolar cells, which synapse onto ganglion cells. Axons of the ganglion cells bundle to form the right and left optic nerves, which conduct visual information to the brain.

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blind spot

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the point at which the optic nerve exits the eye, because no photoreceptors are present there

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fovea

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a small area of the retina, which is densely packed with cones, and is important for high acuity vision

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glaucoma

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the eye cannot adequately drain aqueous humor, so pressure builds in the anterior chmaber and is transmitted to the vitreous humor, leading to increased pressure on the optic nerve. If the pressure is not relieved, this condition can permanently damage the optic nerve and lead to blindness.

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pathway of sound waves through the ear

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outer ear (auricle/pinna + auditory canal) -- tympainic membrane (eardrum) of the middle ear, vibrates at the same frequency as the incoming sound -- the ossicles amplify the stimulus, and transmit it through the oval window -- leads to the fluid-filled inner ear (cochlea and semicircular canals)

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the eardrum

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also called the tympanic membrane; located in the middle ear

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ossicles of the ear

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malleus, incus, and stapes; vibration of the ossicles exerts pressure on the fluid in the cochlea, stimulating the hair cells to transduce the pressure into action potentials.

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inner ear

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consists of the cochlea and semicircular canals (all three are perpendicular to one another)

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cochlea

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contains the organ of Corti, which has specialized sensory cells called hair cells.

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how are action potentials created in the ear?

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vibrating ossicles exert pressure on the fluid in the cochlea, and hair cells transduce the pressure into action potentials which travel via the auditory (cochlear) nerve to the brain for processing.

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endolymph

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a fluid that fills the three semicircular canals of the inner ear

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semicircular canals

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connected at the bases (called the vestibule) to the cochlea; the chamber at the base contains sensory hair cells

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rotation of the head and the ear

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rotation displaces endolymph in one of the semicircular canals, putting pressure on the hair cells in it. This changes the nature of impulses sent by the vestibular nerve to the brain, and the brain interprets the information to determine the position of the head.

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vestibulocochlear nerve

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or cranial nerve VIII is composed of two nerves - the cochlear and vestibular nerves

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the chemical senses

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taste and smell

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taste receptors

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or taste buds; located on the tongue, soft palate, and the epiglottis; they are composed of approximately 40 epithelial cells; outer surface contains a taste pore from which microvilli (taste hairs) protrude.

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location of receptor surfaces for taste

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on the taste hairs

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olfactory membrane

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lies in the upper part of the nostrils over a total area of about 5 cm^2; location of the olfactory receptors

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olfactory receptors

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specialized neurons from which olfactory hairs (or cilia) project; the cilia form a dense mat in the nasal mucosa

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pathway of action potential created by olfactory receptors

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axons from olfactory receptors join to form the olfactory nerves, which project directly to the olfactory bulbs in the base of the brain