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70 Cards in this Set
- Front
- Back
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What is the function of neurons?
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Respond to stimulus by generating an action potential.
Involves the flow of electrical currents across the cell membrane. |
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What are the four stages of action potential?
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1. Resting State
2. Depolarization 3. Repolarization 4. Hyperpolarization |
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Explain Resting State of action potential.
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-70mV
Only leakage channels for Na+ and K+ are open. All voltage gated Na+ and K+ channels are closed. |
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Explain Depolarization of action potential.
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Memrbane potential drops to zero.
Opening of voltage gated Na+ channels. Na+ rushes into cell. Causes membrane polarity to rise to +30mV. |
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Explain Repolarization of action potential.
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Na+ channel shuts.
Causes K+ channel to open. K+ rushes out of the cell. Inside of cell becomes -70mV. |
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Explain Hyperpolarization of action potential.
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Inside membran becomes more negative than resting potential as K+ channels are slow to shut.
Reduces probability of producing a nerve impulse. Resting state re-established by Na+/K+ ATPase Pump. |
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What is the synapse?
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Junction that mediates information transfer from one neuron to another neuron or an effector cell.
Communication based on release and reception of neurotransmitters. Communication in one direction only. Neurotransmitters contained within vesicles in synaptic bulb at axon terminal. |
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Presynaptic Neuron
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Conducts impulses towards the synapse.
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Postsynaptic Neuron
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Transmits impulses away from the synapse.
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What are the external features of the cerebral hemispheres?
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Elevated ridges - gyri.
Shallow grooves - sulci. Deep grooves - fissures. |
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What are the five lobes of the cerebral hemispheres?
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Frontal
Parietal Temporal Occipital Insula |
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What does the left hemisphere control?
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Language, math and logic.
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What does the right hemisphere control?
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Insight, visual-spatial skills, intuition and artistic skills.
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How do the hemispheres communicate?
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Via fiber tracts in the cerebral white matter.
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What are commissures?
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Connect the two hemispheres.
Corpus Callosum largest commissure. |
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What are porjection fibers?
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Connect the hemispheres with lower brain or spinal cord.
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What does the Diencephalon consist of?
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Paired structures - thalamus and hypothalamus.
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Thalamus
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In the central core of the forebrain.
2 lobes with a midline commissure. Roles in sensory reception, organisation and distribution. |
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Hypothalamus
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Autonomic control centre.
Regulates homeostasis. |
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Cerebellum
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Inferior to occipital lobes.
Two hemispheres with three lobes. Receives input from cerebral motor cortex, brainstem nuclei, sensory receptors. |
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Brainstem
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Consists of midbrain, pons, medulla oblongata.
Control autonomic function e.g. respiration, heart rate, blood pressure. |
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Protection of the Brain
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CNS soft tissue, delicate, easily damaged.
Protected by: - bony enclosure - skull. - connective tissure membranes - meninges. - fluid cushion - CSF. |
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Meninges
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Connective tissue membrane that covers CNS structures:
- Dura mater. - Arachnoid mater. - Pia mater. |
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What is the function of the meninges?
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Protects blood vessels and encloses venous sinuses.
Contains CSF. Forms partitions in the skull and anchors brain structures. |
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Function of CSF
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Gives buoyancy to the CNS organs.
Protects the CNS from blows and other trauma. Nourishes the brain and carries chemical signals. |
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Ventricles
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Network of interconnected chambers in the brain through which CSF flows.
Lateral ventricles (2) - superior to thalamus. 3rd ventricle - surrounds middle of thalamus. 4th ventricle - anterior to cerebellum. |
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Spinal Cord
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Connects brain to spinal nerves.
Extends from medulla to upper lumbar vertebrae. Enclosed within vertebral column. Protected by meninges and CSF. 31 pairs of spinal nerves. |
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What does gray matter consist of?
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Dorsal Horns:
- interneurons that synpase with sensory neurons. Ventral Horns: - somatic motor neurons exit (via ventral roots). Dorsal Root: - contain cell bodies of sensory neurons. |
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PNS
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Link between body and brain.
Faciliates the transfer of information to: - monitor the interanl and external environment. - maintain homeostasis. All neural structures outside the brain: - sensory receptors. - peripheral nerves and associated ganglia. - motor endings. |
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Structure of a Nerve
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Cordlike organ of the PNS:
- transmit sensory and motor impulses to and from spinal cord. - bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue. |
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What are the connective tissue coverings of nerves?
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- Endoneurium - loose conective tissue that encloses axons and their myelin sheaths.
Perineurium - coarse connective tissue that bundles fibers into fascicles. Epineurium - tough fibrous sheath around a nerve. |
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Cranial Nerves
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12 pairs of nerves associated with the brain.
- pass through foramina (holes) in skull. Most are mixed in function: - two pairs are purely sensory. Designated names and roman numerals. |
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Cranial Nerve (10) - Vagus
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2 mixed cranial nerves.
Originate from medulla. Widely innervate thorax and abdomen. Carry motor signals to lungs, heart, digestive organs. Carry sensory impulses from same structures as motor neurons. |
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How are spinal nerves connected to spinal cord?
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Dorsal Roots:
- contain sensory neurons. Ventral Roots: - contain motor neurons. |
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What are nerve plexuses?
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Plexuses redistribute fibers from spinal nerves into new peripheral nerves.
Ensure that targets receive their suply of neurons from several spinal nerves. Helps to prevent total loss of motor and sensory function if a spinal nerve is damaged. |
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What is the purpose of motor neurons?
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Carry impulses from CNS to muscles and glands.
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What is the somatic motor division?
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Stimulates skeletal muscle contraction.
Under conscious, voluntary control. Only one motor neuron connects CNS to target muscle. |
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What is the autonomic motor division?
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Initiates motor responses from glands, smooth and cardiac muscle.
Under involuntary control. Controlled by hypothalamus and medulla. Key role in homeostasis. Motor impulses transmitted from CNS to target tissue by a chain of 2 motor neurons. Synapse between 2 neurons in ganglion. |
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What are the two divisions of the ANS?
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Sympathetic
Parasympathetic. |
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What is dual innervation?
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Almost all visceral organs are served by both divisions, but they cause opposite effects.
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What is the sympathetic division of the ANS?
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Mobilizes the body during activity - fight or flight.
Promotes adjustments during exercise, or when threatened: - blood flow is shunted to skeletal muscles and heart. - bronchioles dilate. - liver releases glucose. |
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Where do sympathetic motor neurons exit the CNS?
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Via the thoracic and lumbar regions of the spinal cord.
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What are the distinct ganglia parallel to the vertebral columb called? (Sympathetic)
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Paravertebral symphatetic trunks.
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What is the neurotransmitter used to stimulate target tissue in the sympathetic division of the ANS?
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Noradrenalin.
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What is the purpose of the parasympathetic division of the ANS?
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Promotoes maintenance activities and conserves body energy.
Example = person relaxing after a meal. - blood pressure, heart rate, respiratory rates are low. - gastrointestinal tract activity is high. - pupils are constricted and lenses are accommodated for close vision. |
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Where do motor neurons of the parasympathetic division exit the CNS from?
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Brainstem
Sacral part of spinal cord. Vagus nerve. |
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What is the major neurotransmitter of the parasympathetic division?
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Acetylcholine.
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What are cholinergic fibers?
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Release neurotransmitter ACh.
- all ANS preganglionic axons. - all parasympathetic postganglioic axons. |
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What are adrenergic fibers?
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Release neurotrasmitter NA.
- most sympathetic postganglionic axons. - some exceptions. |
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Receptors for neurotransmitters.
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1. Cholinergic receptors for ACh.
2. Adrenergic receptors for NA: - alpha - beta = effects of NA depend on whcih subclass of receptor predominates on the target organ. |
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What are the three functions of the nervous system?
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Sensory Input - information gathered by sensory receptors about internal and external changes.
Integration - interpretation of sensory input. Motor Output - activation of effector organs (muscles and glands) produces a response. |
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Purpose and components of the CNS?
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Brain and spinal cord.
Integration and command centre. |
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Purpose and components of the PNS?
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Paired spinal and cranial nerves carry messages to and from the CNS.
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What are the two functional divisions of the PNS?
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Sensory (afferent) division.
Motor (efferent) division. |
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What is the sensory (afferent) division?
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Afferent fibers convey impulses from skin, skeletal muscles, joints and visceral organs.
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What is the motor (efferent) division?
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Transmits impulses from the CNS to effector organs.
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What are the two subdivisions of the motor division?
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Somatic (voluntary) nervous system:
Typically under conscious control of skeletal muscles. Autonomic (involuntary) nervous system: No direct consciouscontrol. Regulates smooth muscle, cardiac muscle and glands. Two functional subdivisions: Parasympathetic and Sympathetic. |
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Neurons
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Coordinate body functions.
Communicate via electrical signals (and release of neurotransmitters). |
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Neuroglia (glial cells)
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Supporting cells (provide nourishment and protection).
Oligodendrocytes (CNS) Schwann cells (PNS) |
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Oligodendrocytes
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Branched cells.
Processes wrap CNS nerve fibers, forming insulating myelin sheaths. |
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Schwann Cells
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Surround peripheral nerve fibers and form myelin sheaths.
Insulte and protect the axon. |
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Axon
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Generates and transmits nerve impulses (action potentials) away from the cell body.
Knoblike axon terminals (synaptic knobs or boutons): - secretory region of neuron. - release neurotransmitters to excite or inhibit other cells. |
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Myelin Sheath
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Protein-lipoid sheath around most long axons.
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What is the function of myelin sheath?
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Protect and electrically insulate the axon.
Increase speed of nerve impulse transmission. |
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Details of schwann cells?
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Wrap many times around the axon.
Myelin sheath - concentric layers of schwann cell membrane. Nodes of Ranvier - myelin sheath gaps between adajacent schwann cells. |
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Details of oligodendrocytes?
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Myelin sheath - formed from processes of oligodendrocygts, not the whole cells.
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What is myelination of a PNS axon?
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The schwann cell wraps the axon with layers of insulating myelin sheath (schwann cell membrane).
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What is white matter?
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Dense collections of myelinated fibers.
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What is gray matter?
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Mostly neuron cell bodies and unmyelinated fibers.
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What is the function of neurons?
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Respond to adequate stimulus by generating an action potential (nerve impulse).
Data transmission along a neuron is rapid and it involves the flow of electrical currents across the cell membrane. |
