Neurology Term 6 Exam

over view of the nervous system

endocrine and nervous systems maintain internal coordination

endocrine system

communicates by means of chemical messengers (hormones) secreted into the blood

nervous system

employs electrical and chemical means to send messages from cell to cell

nervous system carries out its task in three basic steps

1. sense organs receive information about changes in the body and ecternal environment and transmit coded messages to the brain and spinal cord (CNS: central nervous system)

2. CNS processes this information relates it to past experiences and determines appropriate response

3. CNS issues commands to muscles and gland cells to carry out such a response

two major subdivisions of nervous system

• central nervous system (CNS)

• peripheral nervous system (PNS)

central nervous system

brain spinal coed enclosed by cranium and vetebral column

peripheral nervous system

• all the nervouse system except the brain and spina cord; composed of nerves and ganglia

• nerve → a bundle of nerve fibers (Axons) wrapped in fibrous connective tissue

• ganglion → a knot like swelling in a nerve where neuron cell bodies are concentrated

visceral motor division

• autonomic nervous system

• carries signals to glands, cardiac and smooth muscle

• its involuntary responses are visceral reflexes

universal properties of neurons

1. excitability (irritability)

2. conductivity

3. secretion

excitability

respond to environmental changes called stimuli

conductivity

respond to stimuli by producing electrical signals that are quickly conducted to other cells at distant locations

secretion

when an electrical signal reaches the end of nerve fiber, the cell secretes a chemical neurotransmitter that influences the next cell

neurosoma

• control center of neuron

• also called soma or cell body

• has a single centrally located nucleus with large nucleolus

• cytoplasm contains mitochondria, lysosomes, golgi complex, inclusions, extensive rough ER and cytoskeleton

myelin sheath

• insulation around a nerve fiber

• formed by oligodendrocytes in CNS and Schwann cells in PNS

• consists of the plasma membrane of glial cells

myelination

• production of the myelin sheath

• begins at week 14 of fetal development proceeds rapidly during infancy

• completed in late adolescence

• dietary fat is important to CNS development

conduction speed

• small unmyelinated fibers → 0.5 to 2.0 m/s

• small myelinated fibers → 3 to 15.0 m/s

• large myelinated fobers → up to 120 m/s

• slow signals set to gatrointestinal tract where speed is less of an issue

• fast signals sent to skeletal muscles where speed improves balance and coordinated body movement

electrical potential

• a difference in concentration of charged particles between one point an another

• living cells are polarized and have a resting membrane potential

• cells have more negative particles on inside of membrane than outside

• neurons have about -70 mV resting membrane potential

electrical current

• a flow of charged particles from one point to another

• in the body currents are movements of ions such as or through channels in the plasma membrane

• gated channels are opened or closed by various stimuli

• enables cell to turn electrical currents on and off

potassium

• has greates influence on RMP

• plasma membrane is more permeable to potassium than any other ion

• leaks freely out (concentration gradient) until electrical charge of cytoplasmic anions attract it back in and equilibrium is reached

• is about 40 times as concentrated in the ICF as in the ECF

• cytoplasmic anions cannot escape due to size of charge (phosphate, sulfates, small organic acids, proteins, ATP, and RNA)

Na/K pump moves 3 sodium out for every 2 potassium it brings in

• works continuously to compensate and leakage and requires great deal of ATP (1 ATP per exchage)

  • 70% of the energy requirement of the nervous system

• necessitates glucose and oxygen be supplied to nerve tissue (energy needed to create the resting potential)

• the exchange of 3 positive charges for only 2 positive charges contributes about -3mV to the cell’s resting membrane potential of -70mV

characteristics of action potential (unlike local potential)

• follows an all-or-none law

• nondecremental: do not weaker with distance

• irreversible: once started, goes to completion and cannot be stopped

refratory period

• the period of resistance of stimulation

• only a small patch of neuron’s membrane is refractory at one time (other parts of the cell can be stimulated

two phases of refractory period

1. absolute refractory period

2. relative refractory period

absolute refractory period

• no stimulus of any strength will trigger AP

• lasts as long as Na+ gates are open then inactivated

relative refractory period

• Only an especially strong stimulus will trigger new AP

• K+ gates are still open, and any effect of incoming Na+ is opposed by the outgoing K+

• generally lasts until hyperpolarization ends

myelinated fibers conduct

signals with saltatory conduction - signal seems to jump from node to node

nodes of ranvier contain

many. voltage gated ion channels while myelin covered internodes contain few

synapses

• a nerve signal can go no further when it reaches the end of the axon

  • triggers the release of a neurotranmitter

  • stimulates a new wave of electrical activity in the next cell across the synapse

neuropeptides

• chains of 2 to 40 amino acids

• stored in secretory granules

• include: cholecystokinin and substance P

• some are produced in GI tract known as the gut brain peptide they cause cravings for certain foods and can be associted with some eating disorders

synapses vary

• some neurtotransmittrs are excitatory, others are inhibitory and sometomes a transmitter’s effect differs depending on the type of receptors on the postsynaptic cell

• some receptors are ligand-gated ion channels and others act through second messengers

acytylcholine is broken down by

acetylcholinesterase (AchE) in the synaptic cleft

for a cell to fire an action potential it must be excited to its threshold level (typically -55mV)

• an excitatory postsynaptic potential (EPSP) is a voltage change from RMP toward threshold

• EPSP usually results from Na+ flowing into the cell

different neurotransmitter cause

different types of postsynaptic potentials in the cells they bind to

a neurotransmitter might

excite some cells and inhibit others, depending on the type of receptors the postsynaptic cells have

summation

the process of adding up postsynaptic potentials and responding to their net effect

where is the calculator of the neuron

axon hillock

presynaptic facilitation

• occurs when one presynaptic neuron enhances another one (opposite of inhibition)

• increases necessary synaptic transmission

• facilitating neuron (cell “F” in figure) releases serotonin

types of neural circuits

• diverging circuit

• converging circuit

• reverberating circuits

• parallel after discharge circuits

diverging circuit

• once nerve fiber branches an synapses with several postsynaptic cells

• one neruon may produce output through hundreds of neurons

converging circuit

• input from many different nerve fibers can be funneled to one neruon or neural pool

• opposite of diverging circuit

reverberating circuits

• neurons stimulate each other in linear sequence but one or more of the later cells restimulates the first cell to start the process all over

• diaphragm and intercostal muscles

parallel after-discharge circuits

input neuron diverges to stimulate several chains of neurons

parkinson disease

• progressive loss of motor function beginning in 50s or 60s - no recovery

• degeneration of dopamine-releasing neurons

  • dopamine normally prevents excessive activity in motor centers (basal nuclei)

  • involuntary muscle contractions

    • pill rolling motion, facial rigidity, slurred speech

    • illegible handwritting, slow gate

parkinsons disease treatment

• drugs and physical therapy

• dopamine precursor (L-dopa) crosses brain barrier; bad side effects on heart and liver

• MAO inhibitos slows neural degeneration

• surgical technique to relieve tremors

spinal cord occupies

• the upper two thirds (2/3) of vertebral canal

• inferior margin ends at L1 or slightly beyond

spinal cord meninges from supperficial to deep

dura mater → arachnoid mater → pia mater

the dura mater

forms the dural sheath that surrounds spinal cord and is seperated from vertebrae by epidural space, It’s in this space that the epidural anesthesia is made (common in childbirth)

arachnoid mater

• adheres to dura and is separated fro pia by fibers spanning the subarachnoid space that is filled with cerebrospinal fluid (CSF)

• lumbar puncture (spinal tap) takes sample of CSF (taken below the medullary cone in that subarachnoid space)

pia mater

delicate membrane that follows contours of spinal cord and continues inferiorly as a fibrous terminal filum that fuses with dura to form coccygeal ligament

gray mater of spinal cord

• central core of gray matter that looks butterfly or H-shaped in cross section

• has a pair of posterior (dorsal) horns

• pair of thicker anterior (ventral) horns

pair of posterior (dorsal) horns

the posterior horn receives sensory nerve fibers from the spinal nerves, (which synapses with interneurons in the posterior horn (posterior dorsal) root of spinal nerve carries only sensory fibers)

pair of thicker anterior (ventral) horns

anterior horn contains large cell bodies of motor neurons which connects with muscle fibers (anterior (ventral) root of spinal nerve carries only motor fibers)

gray commissure

• connects right and left sides

• has central canal lined with epedymal cells and filled with CSF

lateral horns

• visible from T2 through L1

• contains neurons of sympathetic nervous system

corticospinal tracts

• carry signals from cerebral cortex for precise finely coordinated movements

• pyramids → ridges on anterior surface of medulla oblongata formed from fibers on this system

• most fibers decussate in lower medulla forming the lateral corticospinal tract on contralateral side of spinal cord

• some fibers form the anterior (ventral) corticospinal tratc that decends in the ipsilateral side of spinal cord and decissates inferiorly in the spinal cord (like lateral tract, they ultimately control contralateral muscles)

sensory (afferent) nerves → going up

carry signals from sensory receptors to the CNS

motor (efferent) nerves → going down

carry signals from CNS to muscles and glands

mixed nerves

consists of both afferent and efferent fibers

both sensory and motor fibers can also be described as

• somatic or visceral

• general or special

ganglion

• cluster of neurosomas outside the CNS → in PNS

• enveloped in an endoneurium continuous with that of the nerve

among neurosomas are

• bundles of nerve fibers leading into and out of the ganglion

• posterior root ganglion associated with spinal nerves

how many pairs of spinal nerves

31 pairs of spinal nerves (mixed nerves

number of cervical nerves

8 (C1-C8)

number of thoracic nerves

12 (T1-T12)

number of lumbar nerves

5 (L1-L5)

number of sacral nerves

5 (S1-S5)

number of coccygeal nerves

1 (Co1)

where do the spinal nerves exist

• first cervical nerve exits between skill and atlas

• other exit at intervertebral foramina

• C1-C7 → exit above their vertebrae

• C8 and below → exit below the vertebrae

proximal branches

• each spinal nerve is formed from two roots (proximal branches)

• posterior (dorsal) root is sensory input to spinal cord

  • posterior (dorsal) root ganglion - contain the neurosomas of sensoru neurons carrying signals to the spinal cord

  • six to eight enter posterior horn of cord

chicken pox

• common disease of ealy childhood

  • caused by varicella-zoster virus

  • produces itchy rash that clears up without complications

chicken pox virus remains for life in

• the posterior root ganglia

• kept in check by the immune system

shingles (herpes zoster)

• localized disease caused by the virus traveling down the sensory nerves by fast axonal transport when immune system is compromised

• common after age 50

• painful trail of skin discoloration and fluid-filled vesicles along path of nerve

• usually in chest and waist on one side of the body

• pain and itching

• childhood chickenpox vaccinations reduce the risk of shingles later in life

nerve plexuses

• anterior rami branch and anatomose repeatedly to form five nerve plexuses

  1. cervical plexus

  2. brachial plexus

  3. lumbar plexus

  4. sacral plexus

  5. coccygeal plexus

cervical plexus

• in the neck C1 to C5

• supplies neck and phrenic nerve to the diaphragm

brachial plexus

• near the shoulder C5 to T1

• supplied upper limb and some of shoulder and neck

• median nerve - carpal tunnel syndrome

lumbar plexus

• in the lower back L1 to L4

• supplies abdominal wall, anterior thigh and genitalia

sacral plexus

• in the pelvis, L4, L5, and S1 to S4

• supplies remainder of lower trunk and lower limb

coccygeal plexus

S4, S5 and Co1

ulnar nerve comes out of root

C8, T1

median nerve comes out of root

T1, C8, C7, C6, C5

radial nerve comes out of root

C8, C7, C6

axillary nerve comes out of root

C8, C7, C6

musculocutaneous nerve comes from root

C7, C6

illiohypogastric nerve comes from root

L1

ilioinguinal nerve comes from root

L1

genitofemoral nerve comes from root

L1, L2

lateral femoral cutaneous nerve comes from root

L2, L3

femoral nerve comes from root

L2, L3, L4

obturator nerve comes from root

L2, L3, L4

pathway of a somatic reflex arc

• somatic receptors

  • skin, muscles or tendons

• afferent nerve fibers

  • carry information from receptors to posterior horn of spinal cord or to the brainstem

• integrating center

  • a point of synaptic contact between neurons in gray matter of cord or brainstem determines whether efferent neurons issue signal to muscle

• efferent nerve fibers

  • carry motor impulses to muscles

• effectors

  • the muscles that cary out the response

reciprocal inhibition

reflex phenomenon that prevents muscles from working against each other by inhibiting antagoist when agonist is excited

flexor reflex

the quick contraction of flexor muscles resulting int the withdrawl of a limb from an injurious stimulus (like a hand on a hot stove)

tendon organs

• proprioceptors in a tendon near its junction with a muscle

• golgi tendon organ: 1mm long, nerve fibers entwined in collagen fibers of the tendon

cerebrum

• 83% of brain’s volume

• pair of cerebral hemispheres marked by gyru and sulci

• longitudinal fissure seperates L and R hemispheres

• connected by a thick bundle of nerves: corpus collosum

neural plate

• sinks and thickens to form the neural groove with raised neural folds

• neural folds fuse along midline, like closing a zipper

embryo → fully developed

• forebrain/prsencephalon

  • telencephalon → cerebrum

  • diencephalon → thalamis, hypothalamus

• midbrain/mesencephalon

  • mesencephalon → midbrain

• hindbrain/rhombencephalon

  • metencephalon → pons, cerebellum

  • myelencephalon → medulla oblongata

meninges in the brain

• three connective tissue membranes envelop the brain (between the nervous tissue and bone)

• meninges protect the brain and provide a structural framework for its arteries and veins

layers of meninges in the brain from superficial to deep

dura mater (2layers) → arachnoid mater → pia mater

ventricles of the brain

• the brain has 4 internal chambers called ventricles

• 2 lateral ventricles, 3rd ventricle, and a 4th ventricle

2 lateral ventricles

• one in each cerebral hemisphere

• connect to 3rd ventricle by the interventricular foramina (“foramina of munro”)