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187 Cards in this Set

  • Front
  • Back

Structurally, the nervous system is divided into

Central nervous system (CNS) and Peripheral nervous system (PNS)

Central nervous system consists of the

Brain and spinal cord


Peripheral nervous system consists of the

Cranial and spinal nerves

Peripheral pathways are either

Afferent (ascending) or Efferent (descending)

Afferent pathways carry _______ impulses _______ the CNS

sensory impulses toward the CNS

Efferent pathways carry _______ impulses ________ the CNS

motor impulses away from the CNS

Efferent pathways innervate _____________

Effector organs such as skeletal, cardiac, and smooth muscle, as well as glands

The PNS is divided into what two systems?

Somatic and autonomic

Somatic nervous system

Consists of motor and sensory pathways



Regulates voluntary motor control of skeletal


muscle

Autonomic nervous system

Consists of motor and sensory pathways



Regulates viscera through involuntary control


of organ systems

Autonomic nervous system is divided into what two systems?

Sympathetic and parasympathetic

Two basic cells that comprise nervous tissue

Neurons and neuroglial cells

Neuron

Primary information / communication cell of


the nervous system



Fuel source is glucose, but insulin is not


required for glucose uptake in the CNS



Consist of neurofilaments, neurotubules,


neurofibrils, and Nissl substances

Neuroglial cells

Found in CNS and PNS



Provide structural support & nutrition for


neurons, remove debris, increase speed of


nerve impulses, and help process and store


information (i.e., memory)

Neurofilaments and neurofibrils

Responsible for structural support and movement of neuron processes

Neurotubules

Help to transport cellular products

Nissl substances

Contain endoplasmic reticulum and ribosomes and are involved in protein synthesis

Does the CNS initially have more or just enough neurons

More. Extra neurons that do not become in functional systems die.

Can neurons divide after birth?

Some. Olfactory neurons divide throughout life.

Three components of a neuron

- Cell body (soma)


- Dendrites


- Axons

Where are most neuronal cell bodies located?

Within the CNS

Nuclei

Dense, packed neuronal cell bodies in the CNS

Ganglia or plexuses

Groups of neuronal cell bodies located in the PNS

Dendrites

Carry impulses toward the cell body

Dendritic zone

The receptive portion of a neuron that receives a stimulus and continues further conduction

Axons

Carry nerve impulses away from the cell body

Axon hillock

Cone-shaped, organelle free area where the axon leaves the cell body

Fascicles

Axons that are bundled together in large nerves

Where does the action potential begin in an axon?

In the initial segment of the axon

Typically, how many axons does a neuron have?

One

Myelin sheath

Insulating membrane that surrounds axons

Endoneurium

Connective tissue that surrounds the myelin sheath

Neurilemma

Located between the endoneurium and myelin sheath. It contains the Schwann cell that produces the myelin sheath.

Nodes of Ranvier

Uninsulated gaps in the myelin sheath where


electrical impulses can be conducted



Allows increased velocity of neuronal


conduction



Known as saltatory conduction

Unmyelinated neurons

When Schwann cells are loosely wrapped


around axons



Conduction velocity is not increased

Where does axonal branching occur?

At the nodes of Ranvier

Divergence

When branching axons influence many different neurons

Convergence

When numerous branching axons converge on and influence only one or a few neurons

Examples of demyelinating disorders (problems with the myelin sheath)

- Multiple sclerosis



- Guillain-Barre syndrome

Does axon size influence conduction rate?

Yes, larger axons transmit impulses faster.

Four types of neurons

- Unipolar



- Pseudo unipolar



- Bipolar



- Multipolar

Unipolar neurons

Have one process that branches shortly after


leaving the cell body



Can be found in the retina

Pseudo unipolar neurons

Have one process with the dendritic portion


extending away from the CNS and the axon


projects into the CNS



Typical of sensory neurons in the cranial and


spinal nerves

Bipolar neurons


Has a distinct dendrite process and a distinct


axon process arising from the cell body.



Connects to rods / cones in the retina

Multipolar neurons

- Most common



- Have multiple dendrites and a single axon



- Typical of motor neurons

Three types of neurons

1. Sensory (afferent, mostly unipolar)



2. Associational (interneurons, multipolar)



3. Motor (efferent, multipolar)


Sensory neurons

Carry impulses from peripheral sensory receptors to the CNS

Associational neurons (interneurons)

Transmit impulses from neuron to neuron (i.e.,


sensory to motor neurons)



Also involved in cognitive function


Motor neurons

Transmit impulses away from the CNS to an effector organ

Types of neuroglial cells

- Astrocytes



- Oligodendrocytes



- Ependymal cells



- Microglia



- Schwann cell (neurolemmocyte)

Astrocytes

Fill spaces between neurons and surround blood vessels in the CNS

Oligodendrocytes

- Function to deposit myelin within the CNS



- Counterpart to the Schwann cell

Ependymal cells

Line the CSF filled cavities of the CNS

Microglia

Remove debris (phagocytosis) in the CNS

Schwann cell (neurolemmocyte)

- Wraps around and covers axons in the PNS



- Form and maintain the myelin sheath

Wallerian degeneration

When an axon is severed, causing the axon


distal to the cut to degenerate and


disappear.



The myelin sheaths reform into Schwann


cells that align in a column between the cut


and the effector organ



- At the proximal end repair occurs back to


the next node of Ranvier only.



The cell body swells and disperses Nissl


substance



7-14 days after the trauma new terminal


sprouts arise from the proximal segment


may enter the remaining Schwann cell


pathway



Limited to myelinated fibers and typically


only occurs in the PNS

Why is regeneration of axons limited in the CNS?

Scar tissue forms easier and the oligodendrocytes form myelin differently

What factors effect nerve regeneration?

The closer the injury to the cell body, the


greater the chance the nerve will die



Inflammatory response to injury



Scar tissue formation



Type of injury


- Crush injuries are less damaging than cut


injuries

Synapse

Regions between adjacent neurons

How are impulses transmitted across a synapse?

By chemical and electrical conduction

Neurons that conduct impulses toward the synapse

Presynaptic neurons

Neurons that conduct impulses away from the synapse

Postsynaptic neurons

Four types of connections between pre- and post-synaptic neurons

1. Between axons (axo-axonic)



2. From axon to cell body (axo-somatic)



3. From axon to dendrite (axo-dendritic)



4. Between dendrites (dendro-dendritic)

Neurotransmitter

Chemical that conducts impulses across the


synapse



Often formed in the neuron



Gets transported to a synaptic knob (bouton)


of the presynaptic neuron's axon



Is stored in synaptic vesicles w/in the knobs



Released into the synaptic cleft by action


potentials in the presynaptic neuron



Binds to neurotransmitter receptors on the


postsynaptic neuron

Can neurons synthesize more than one neurotransmitter?

Yes

Can postsynaptic membranes have more than one type of neurotransmitter receptor?

Yes

Name a few neurotransmitters

Norepinephrine



Acetylcholine



Dopamine



Histamine



Gamma-aminobutyric acid (GABA)



Serotonin

Two scenarios for the binding of a neurotransmitter at a receptor site

Postsynaptic neuron may be excited


(depolarized), known as excitatory


postsynaptic potentials (EPSP's)



Postsynaptic neuron may be inhibited


(hyperpolarized), known as inhibitory


postsynaptic potentials (IPSP's)

What affects whether or not an action potential will occur?

The number and frequency of potentials the postsynaptic neuron receives (known as summation). A single EPSP will not induce an action potential

Temporal summation

The effects of successive, rapid impulses received from a single neuron on the same synapse

Spatial summation

The combined effects of impulses from a number of neurons on a single synapse at the same time

Facilitation

The effect EPSP's on the plasma membrane potential

Three major divisions of the brain based on embryonic origin

Forebrain - formed by the 2 cerebral hemispheres



Midbrain



Hindbrain - includes the cerebellum, pons, and medulla oblongata

What parts of the brain make up the brainstem?

The midbrain, medulla oblongata, and pons

What is the function of the brainstem?

Connects the brain hemispheres, cerebellum, and spinal cord

Reticular formation

A collection of nerve cell bodies (nuclei) w/in the brainstem that regulates vital reflexes such as CV function and respiration. Also essential for maintaining wakefulness and can be involved in motor movements.

Plasticity

Holds that the CNS is capable of change. For example, in children w/ brain damage some functional areas may relocate to other areas of the brain.



Plasticity decreases with age.

Cerebral cortex

Largest portion of the brain



Contains cell bodies and dendrites (gray


matter)


Telencephalon

Part of the forebrain, and consists of the cerebral cortex and basal ganglia

Gyri

Numerous convolutions on the surface of the cerebrum. Increase the cortical surface area.

Sulci

Grooves between gyri

Fissures

Deep grooves between gyri

Gray matter

Located in the cerebral cortex



Receives, integrates, stores, and transmits


information

White matter

Lies beneath the cerebral cortex



Composed of myelinated nerve fibers



Sends neuronal messages throughout the


nervous system and body

Longitudinal fissure

Separates the cerebral hemispheres

Prefrontal area

Responsible for goal-oriented behavior, ability to concentrate, short term or recall memory, and elaboration of thought and inhibition on the limbic (emotional) areas of the CNS

Premotor area (Brodman area 6)

Involved in programming motor movements



Also contains neurons that contribute to the


basal ganglia system (extrapyramidal)

Primary motor area (Brodman area 4)

- Located at precentral gyrus



- Forms the primary voluntary motor area



- Causes specific body muscles to move

Contralateral control

How cerebral impulses control function on the opposite side of the body

Broca speech area

Usually on the left hemisphere



Responsible for motor aspects of speech



Damage results in expressive aphasia or


dysphasia

Parietal lobe

Contains major area for somatic sensory input


such as storage, analysis, and interpretation of


stimuli

Association fibers

Facilitates communication between motor and sensory areas

Occipital lobe

- Contains primary visual cortex.



- Receives input from the retinas.

Temporal lobe

Primary auditory cortex



Contains Wernicke's area. Damage can cause


receptive aphasia or dysphasia.



Also major area for long-term memory,


balance, taste, and smell

Corpus callosum

Connects the 2 cerebral hemispheres and is


essential in coordination of activities between


the hemispheres



Can be cut as a last resort to prevent epileptic


loci (site of seizure activity) from spreading to


the other hemisphere. Cutting it can cause


temporary aphasia and paralysis.

Basal ganglia

- Major cerebral nuclei



- Include the corpus striatum and amygdala

Basal ganglia system (extrapyramidal system)

Exerts a fine-tuning effect on motor movements



Defects of basal ganglia cause diseases like


Parkinson's and Huntington's



Disorders are characterized by involuntary


or exaggerated motor movements

Limbic system

Is an extension or modification of the


olfactory system



Effects primitive behavioral responses,


visceral reaction to emotion, feeding


behaviors, biologic rhythms, and the sense


of smell



Consolidates memory through a


reverberating circuit

Diencephalon

- Surrounded by the cerebrum



- Made up of 4 divisions: Epithalamus,


thalamus, hypothalamus, and subthalamus

Epithalamus

Creates the roof of the 3rd ventricle



Contains pineal body, which secretes


melatonin and maintains circadian rhythms


of the sleep wake cycle

Thalamus

Largest part of diencephalon



Surrounds the 3rd ventricle



Major integrating center for afferent


impulses to the cerebral cortex with the


exception of olfaction



Serves as a relay center for sensory aspects


of motor info from the basal ganglia and


cerebellum to cortical motor areas



Cerebral cortical info also projects to the


thalamus, creating reverberating circuits

Hypothalamus

Forms the base of the diencephalon



Maintains a constant internal environment


and implements behavioral patterns



Controls ANS function, regulates body temp,


regulates endocrine system function, and


regulates emotional expression



Exerts influence via endocrine system and


neural pathways

Subthalamus

Contains subthalamic nucleus, which is part of the basal ganglia system

Midbrain (mesencephalon)

Controls voluntary and involuntary visual


and auditory motor movements (i.e.,


tracking a finger with the eyes or moving


the head to hear better)



Contains substantia nigra, which synthesizes


dopamine. Substantia nigra dysfunction is


related to Parkinson's and drug addiction.



Contains tracts of 3rd and 4th cranial nerves


and is traversed by the cerebral aqueduct


that carries CSF.

Metencephalon

Major structures include the cerebellum and pons

Cerebellum

Has 2 cerebellar hemispheres covered with convolutions called folia



Hemispheres are connected by the vermis (worm)



Responsible for conscious and unconscious muscle synergy and for maintaining posture and balance



Damage causes same sided (ipsilateral) loss of equilibrium, balance, and motor coordination



It has ipsilateral control of the body

Pons

Transmits info from the cerebellum to the brainstem nuclei and relays motor info from the cerebral cortex to the contralateral cerebral hemisphere



Controls respiration



Contains nuclei of cranial nerves V - VIII

Myelencephalon

Contains the medulla oblongata



Controls reflex activities such as heart rate, respirations, BP, coughing, sneezing, swallowing, and vomiting



Contains nuclei of cranial nerves IX - XII



A major portion of the descending motor pathways crosses to the contralateral side (decussates) at the inferior medulla oblongata

Spinal cord

Protected by vertebral column



Is a long nerve tract connecting the brain and body



Conducts somatic and autonomic reflexes, provides motor pattern control centers, and serves as a sensory and motor modulation center



Ends at the 1st or 2nd lumbar vertebrae in adults

Conus medullaris

The cone shaped end of the spinal cord

Cauda equina

Bundle of spinal nerves at the end of the spinal cord

Filum terminale

Thin filament anchor going from the conus medullaris to the coccyx

Sections of the spinal cord

8 cervical



12 thoracic



5 lumbar



5 sacral



1 coccygeal

Gray matter of the spinal cord

Appears as a butterfly shape in a cross-section specimen



Divided into 3 regions:



- Posterior (dorsal) horn


- Gray (lateral) horn


- Anterior (ventral) horn

Posterior horn

Comprised of interneurons and axons from sensory neurons



Contains the substantia gelatinosa, which is involved in pain transmission

Gray horn

Contains cell bodies involved with the ANS

Anterior horn

Contains nerve cell bodies for efferent pathways leaving the spinal cord by way of spinal nerves

White matter of spinal cord

Surrounds the gray matter



Forms ascending and descending pathways called spinal tracts



Divided into 3 columns:



- Anterior column


- Lateral column


- Posterior column

Spinothalamic tract

Carries nerve impulses from the spine to the thalamus

Reflex arcs

Respond to stimuli and provide protective circuitry for motor output



Requires a receptor, an afferent (sensory) neuron, and efferent (motor) neuron, and an effector muscle or gland

Spinal cord afferent pathways

Transmit info from peripheral receptors with the info terminating in the cerebral or cerebellar cortex, or both

Spinal cord efferent pathways

Primarily relay info from the cerebrum to the brainstem or spinal cord

Upper motor neurons

Motor pathways completely contained w/in the CNS



Primary roles are to direct, influence, and modify reflex arcs, lower level control centers, and motor (and some sensory) neurons



Form synapses with interneurons, which then form synapses with lower motor neurons before projecting to the periphery



Damage initially causes paralysis but partial recovery can occur w/in days or weeks

Lower motor neurons

Are cranial and spinal efferent neurons



Responsible for direct influence on muscles



Their cell bodies lie in the gray matter of the spinal cord but their processes extend into the PNS



Damage leads to permanent paralysis most of the time unless peripheral nerves are able to regenerate

Motor units

A motor neuron and the skeletal muscle it stimulates

Neuromuscular (myoneuronal) junction

The junction between the axon of the motor neuron and the plasma membrane of the muscle cell

Four clinically relevant motor pathways (tracts)

1. Lateral corticospinal


2. Corticobulbar


3. Basal ganglia


4. Vestibulospinal

Corticobulbar tract

Composed of the upper motor neurons of the cranial nerves



Is a 2 neuron white matter motor pathway connecting the cerebral cortex to the brainstem



Decussates in the medulla to form the lateral corticospinal tract of the spinal cord



Innervates cranial motor nuclei for the eyes, face, tongue, throat, and neck movement

Lateral corticospinal tract

Is a descending motor pathway that begins in the cerebral cortex, decussates in the pyramids of the lower medulla and proceeds down the contralateral side of the spinal cord.



It's axons (upper motor neurons) leave the tract through the anterior horn of the spinal cord to go to specific interneurons or motor neurons



It controls fine movement of ipsilateral limbs

Which cranial motor nerves receive contralateral innervation?

Facial (spinal), accessory, and hypoglossal

Basal ganglia

Modulate motor movement by inhibiting and exciting spinal activity

Vestibulospinal tract

An extrapyrimidal tract



Causes the extensor muscles of the body to rapidly contract. Is most dramatic when someone falls backwards.

3 clinically relevant sensory (afferent) pathways

1. Posterior (dorsal) column


2. Anterior spinothalamic


3. Lateral spinothalamic


Posterior dorsal column pathway

Carries upper / lower body fine touch, two point discrimination, and proprioceptive info



Formed by a 3 neuron chain

Anterior and lateral spinothalamic pathways

Responsible for vague touch, pain, and temperature

Galea aponeurotica

A thick, fibrous band of tissue overlying the cranium between the frontal and occipital muscles



Adds protection to the bony skull

Subgaleal space

Blood can be shunted here in cases of ICP



Common site for placement of wound drains after IC surgery

3 protective membranes surrounding the brain and spinal cord

1. Dura mater


2. Arachnoid


3. Pia mater



Collectively these are known as the meninges

Dura mater

Composed of 2 layers with venous sinuses between them



Outer layer is the periosteum



Inner layer (dura or meningeal layer) forms a rigid, double thickness membranous plate that supports and separates brain structures. Compression against these membranes can cause damage to brain structures.

Falx cerebri

One of the membranous plates of the dura mater



Dips between the cerebral hemispheres at the longitudinal fissure

Tentorium cerebelli

One of the membranous plates of the dura mater



Separates the cerebellum from the cerebrum

Arachnoid membrane

Located below the dura mater



Has a filmy, weblike structure



Subdural space

Lies between the dura and arachnoid



Small bridging veins w/out much support traverse this space and can cause subdural hematomas if damaged

Subarachnoid space

Lies between the arachnoid and pia mater



Contains CSF



Damage to intracranial vessels can cause subarachnoid hemorrhage. This causes meningeal irritation that results in neck stiffness, a positive Kernig sign, and lower back pain

Pia mater

Closely adheres to the surface of the brain and spinal cord



Supports blood vessels that serve brain tissues

Choroid plexuses

Produce CSF



Arise from the pia mater

Denticulate ligaments

Extensions of the meninges that anchor the spinal cord to the vertebrae

Epidural space

Between the dura mater and the skull



Common place for epidural hematomas as a result of falls

CSF

A clear, colorless fluid that the intracranial and spinal cord structures float in to protect them from jolts and blows



Also prevents the brain from tugging on meninges, nerve roots, and blood vessels



Gets reabsorbed into venous circulation through arachnoid villi



Samples are obtained by lumbar puncture in the subarachnoid space or by placing an intraventricular catheter

Vertebral column

Composed of 33 vertebrae



- 7 cervical


- 12 thoracic


- 5 lumbar


- 5 fused sacral


- 4 fused coccygeal

Intervertebral disc

Between each interspace except at the fused sacral and coccygeal vertebrae



Absorbs shocks to prevent vertebral damage



Damage can cause disc rupture or herniation

What percent of cardiac output does the brain receive each minute?

20%

What is a primary regulator of blood flow in the CNS, causing vasodilation and ensuring good blood supply?

CO2

From where does the brain receive its arterial blood supply?

1. Internal carotid arteries


2. Vertebral arteries

Arterial circle (Circle of Willis)

Compensates for reduced blood flow

Blood brain barrier

Cellular structures that selectively inhibit certain substances in the blood from entering the spaces of the brain or CSF

How many pairs of spinal nerves are there?

31

Mixed nerves

Spinal nerves. They are called this b/c they have both sensory and motor neurons.



The sensory and mother neurons converge to form one spinal nerve . They then divide into anterior and posterior rami (branches).



The anterior rami branch into peripheral nerves and the posterior rami are distributed to specific areas of the body.



So, sensory signals arise from specific sites associated with a specific spinal cord segment.

Dermatomes

Specific areas of skin innervation at spinal cord segments.

Cranial nerves

Categorized as peripheral nerves



Most are mixed, but some are purely motor or purely sensory



Arise from nuclei in brain and brainstem

Motor component of the ANS

Is a 2 neuron system



Consists of pre- (myelinated) and post- (unmyelinated) ganglionic neurons



Coordinates / maintains steady state among visceral organs and glands



Is an involuntary system



Divided into sympathetic and parasympathetic systems

The sympathetic nervous system functions to

Mobilize energy stores in times of need (i.e., fight or flight)



Epi and norepi are mediators of fight or flight



Adrenergic transmission

From where does the SNS receive innervation?

From T1 - L2 (thoracolumbar division)

Preganglionic axons of the SNS

Form synapses in the sympathetic ganglia



Form pathways called splanchic nerves, which lead to collateral ganglia

Parasympathetic nervous system functions to

Conserve and restore energy



Preganglionic fibers travel to ganglia close to organs they innervate before forming synapses with postganglionic neurons

From where does the PNS receive innervation?

In the cranial nerve region and sacral region of the spinal cord (craniosacral region)

Acetylcholine

Is a neurotransmitter



Released by sympathetic preganglionic fibers and parasympathetic pre- and post-ganglionic fibers



Cholinergic transmission

Name some catecholamines

1. Epinephrine


2. Norepinephrine


3. Dopamine

What gland physiologically and biochemically resembles the SNS and releases catecholamines?

Adrenal medulla gland

What are the 2 types of adrenergic receptors?

Alpha and beta

What action is produced by alpha adrenergic receptors?

Alpha 1: Excitation and stimulation



Alpha 2: Relaxation or inhibition

What action is produced by beta adrenergic receptors?

Beta 1: Increased HR and contractility and the release of renin from the kidneys



Beta 2:



Beta 3: Mediate lypolysis and thermogenesis and are up-regulated in CV disease

Primary response of norepinephrine

Stimulation of Alpha 1 adrenergic receptors that cause vasoconstriction

What are the Dopamine receptors?

D1 - D5

What are the functions of Dopamine receptors?

Pleasure


Motivation


Cognition


Memory


Learning


Fine motor control

Does epi cause vasoconstriction or vasodilation?

Vasodilation

What are the effects on the GI system with SNS versus PNS stimulation?

SNS: Decreased peristalsis



PNS: Increased peristalsis

CT scan

Creates 2 dimensional images from multiple x-rays using computer assist



Capable of showing find distinctions in shape, size, and densities of various tissues



MRI

Uses a magnetic field instead of x-rays



Able to provide reconstruction of images in 3 views

PET scan

Uses CT imaging and injectable radioactive substances or inhaled gases to produce images



The injected or inhaled substances deposit into tissues, showing physiologic and metabolic processes

Brain scan

Radionuclide substances are introduced into the bloodstream for tissue uptake and evaluation

Isotope cisternography

Radionuclide imaging technique used to evaluate CSF flow.

Angiography

A small catheter is introduced at the femoral artery



Contrast dye is injected



Serial x-rays are then taken



Flow of the dye is evaluated

Myelogram

Evaluates intraspinal anatomy



Radiographic dye is placed in the spinal region



X-rays are then taken



Flow of the dye is evaluated

Echoencephalography (ultrasound)

Uses sound waves to evaluate the brain

Electroencephalograph (EEG)

A recording of electrical impulses of the brain via scalp electrodes



Helpful in locating origins of seizure activity and in determining if a person is brain dead

CSF analysis

Used to determine CSF pressure, constituents such as protein and electrolytes, and for cultures