Neuro A&P Review

Nervous System

● CNS

– Brain

– Spinal cord

● PNS

– Cranial Nerves

– Spinal Nerves

● Afferent (sensory) pathways

● Efferent (effector/motor) pathways

Peripheral Nervous System

● Functionally

– Somatic system

– Autonomic system● Sympathetic

● Parasympathetic

Nervous Tissue

● Neuron

● Supporting Cells

– Astrocytes (multiple roles)

– Oligodendria (form myelin in CNS)

– Schwann cells (form myelin in PNS)

– Microglia (CNS macrophage)

– Ependymal (lines ventricles; forms CSF)

Neuron

Tracing the Neural Pathway

● http://www.pfizer.com/brain/dlgame.html

● Dendrite receives stimuli

– Initiates depolarization at cell body

– Electrical impulse jumps from node to node on axon

– At end of axon, reaches axon terminal

– Terminal releases neurotransmitters.

Initiation of Neural Impulse

● A single neuron may synapse with 50,000 other

neurons

– Each secretes a neurotransmitter or neuropeptide● Hundreds of possible chemicals

● Some excitatory

● Some inhibitory

● Varying strength

– Neuron must interpret this cacophony and decide...● To depolarize or not to polarize... that is the question

Nerve Injury and Regeneration

● Axon is severed

– Distal to injury● Axon disintegrates

● Myelin sheath unwinds into Schwann cells and line path

– Proximal● Disintegration to the next node of Ranvier

● Cell body swells

● Begins to grow from stump of axon down Schwann path

● Limited by scar tissue

Brain

● Cerebral cortex (“rind”) – gray matter– Frontal– Parietal– Temporal– Occipital– Wernicke’s area – receptive aphasia– Broca’s area – expressive aphasia

Brain

● Basal ganglia: motor function● Thalamus: relay station● Hypothalamus: HR, BP, sleep, etc.● Cerebellum: motor coordination● Brain stem

– Midbrain– Pons– Medulla: respiration, heart, GI function, CN 8 -

12

Meninges

● 3 membranes surrounding brain and spinal cord

– Dura mater – 2 layers● Periosteum (next to cranium) (epidural space)

● Inner dura (meningeal layer)

● Subdural space between dura mater and next layer

– Arachnoid membrane● Follows contours of brain but not sulci

● Subarachnoid space between arachnoid and next layer

– Pia Mater● Delicate, follows sulci and fissures

CSF and Ventricles

● Similar to plasma

● Circulates in ventricles and subarachnoid space

(125 – 150 ml) at any one time

● Brain floats in it

– Cushions against jarring and jolting

– Prevents pulling on meninges and blood vessels

Blood Supply

● Brain receives 20% of cardiac output

● Collateral circulation

– Internal carotid

– Vertebral arteries

– Join in circle of Willis

● Venous drainage

– Does not parallel arterial supply

– Venous plexuses and dural sinuses drain into internal

jugular vein

Neurotransmitters● Multipurpose

– Depends on post-synaptic neuron and receptor type

● Acetylcholine: multipurpose

– Crosses neuromuscular junction of motor neurons

– Released by both preganglionic sym & parasympa

– Released by postganglionic parasympathetic fibers● Cholinergic fibers

Neurotransmitters● Norepinephrine

– Released by posganglionic sympathetic fibers● Adrenergic fibers

– Released by adrenal glands

● Function of catecholamines varies by receptor and tissue of receptor

– α1 receptor most common

– α2 receptor cause inhibition/relaxation

– β1 heart and kidney

– β1 all other beta receptors

Functions of Autonomic System

● Generally

– Sympathetic stimulation promotes protection of host● Increase BP, HR, glucose

● Increase muscle blood flow and stimulation

● Decrease renal flow and digestion

– Parasympathetic stimulation promotes rest, tranquility

and maintenance functions● Digestion

● Secretion of enzymes

– Action is often antagonistic

Aging

● Extremely complex

● How much is aging, and how much is disease?

● Brain

– Decreased weight and size

– Increased adherence of dura mater to skull

– Fibrosis of meninges

– Widened sulci

– Enlarged ventricles

Cellular Changes with Age● Decrease in number of neurons

– Not consistent with cognitive loss

– Implications and reason are unknown

● Cellular changes

– Dendrite changes

– Lipofuscin deposition (Fatty deposits)

– Neurofibrillary tangles (abnormal proteins)

– Senile plaques (nerve degeneration)● Last two are accelerated in Alzeimer's

– Changes is neurotransmitter function

Tests of Nervous Function

● X-ray: primarily for bony structures

● CT: 2-D recreation from multiple X-rays

– Structures, tumors, hemorrhage (with or without

contrast)

● MRI: magnetic field; soft tissue analysis

● MRA (angiography): visualization of blood

vessels (stroke and TIA)

● PET: injection of radioactive substances; detects

positrons; indicates physiologic processes

Tests of Nervous Function

● Brain scan: uptake of radioactive isotopes

● Cerebral angiography

● Myelography: x-ray with subarachnoid dye

● Echoencephalography (ultrasound)

● Electroencephalography (EEG): seizures

● Evoked potentials

● CSF analysis: protein, blood, organisms

Spinal Cord

● Nerve cell bodies arranged in “horns”● Nerve pathways cross in the spinal cord

– Eg. Sensation of the left side of the body enters the left dorsal horn, and crosses to the right ventral horn and travels to right hemisphere

● Sensation– Spinothalamic tract: pain, temperature, crude and light

touch– Posterior columms: does not cross sides; position,

vibration, finely localized touch