Anatomy - Nervous system

What are the functions of the nervous system?

• Sense organs receive info

• Brain and spinal cord determine responses

• Brain and spinal cord issue commands to glands and muscles

What are the sensory and motor divisions in the PNS?

• Sensory (afferent) divisions (receptors to CNS)

  • Visceral sensory and somatic sensory division

• Motor (efferent) division (CNS to effectors)

  • Visceral motor division (ANS); effectors: cardiac, smooth, glands

    • Sympathetic division (fight or flight)

    • Parasympathetic division (digestion)

  • Somatic motor division; effectors: skeletal

What are the 2 major anatomical and functional subdivisions?

• Central nervous system (CNS)

  • Brain and spinal cord enclosed in bony coverings

• Peripheral nervous system (PNS)

  • Nerve

  • Ganglion

What is a nerve?

Bundle of axons in connective tissue

What is a ganglion?

The swelling of cell bodies in a nerve

What are three functional properties found in all neurons?

• Excitability (irritability)

  • Responds to changes in the body and external environment stimuli

• Conductivity

  • Produce traveling electrical signals between cells

• Secretion

  • When electrical signal reaches end of nerve fiber, chemical neurotransmitters cross gaps

Define the three most basic functional categories of neurons

• Sensory (afferent) neurons

  • Detect changes in body and external environment

    - Information transmitted into brain or spinal cord

• Interneurons (association neurons)

  • Lie between sensory and motor pathways in CNS

  • 90% of our neurons are interneurons

  • process, store, and retrieve information

• Motor (efferent) neuron

  • Send signals out to muscles and gland cells

  • Organs that carry out responses called effectors

Identify the parts of a neuron

• Cell body = soma

• Small dendrites receive signals

• Single axon = (nerve fiber) arise from axon hillock for rapid conduction

What are four structural classes of neurons? Where are they located?: Multipolar neurons

• Brain

• Spinal cord

What are four structural classes of neurons? Where are they located?: Bipolar neurons

• Sensory (ear and nose)

• Retina

What are four structural classes of neurons? Where are they located?: Unipolar neurons

• Single process leaving soma

• Carries single to spinal cord (touch or pain)

  • Skin

What are four structural classes of neurons? Where are they located?: Anaxonic neurons

• No axons: multiple dendrites

• Do not produce action potential

• Communicate to local cells through dendrites

How do neurons transport materials (proteins, organelles, etc.) between the cell body and tips of the axon?

• Anterograde - away from soma and down the axon

• Retrograde - up the axon and toward the soma

What are the 6 types of cells that aid neurons and their functions?: Oligodendrocytes

Form myelin sheath in brain and spinal cord, insulates

What are the 6 types of cells that aid neurons and their functions?: Ependymal cells

Line cavities of brain and spinal cord; secrete and circulate cerebrospinal fluid

What are the 6 types of cells that aid neurons and their functions?: Microglia

Phagocytize and destroy microorganisms, foreign matter, and dead nervous tissue

What are the 6 types of cells that aid neurons and their functions?: Astrocytes

Cover brain surface and nonsynaptic regions of neurons; form supportive framework in CNS; induce formation of blood-brain barrier

What are the 6 types of cells that aid neurons and their functions?: Schwann cells

Form neurilemma around all PNS nerve fibers and myelin around most of them; aid in regeneration of damaged nerve fibers

What are the 6 types of cells that aid neurons and their functions?: Satellite cells

Surround somas of neurons in the ganglia; provide electrical insulation and regulate chemical environment of neurons

What is myelin?

Insulating layer around a nerve fiber

What is the role of myelin in the PNS?

Hundred of layers wrap the axon

• Outermost coil → schwann cell (neurilemma)

What is the role of myelin in the CNS?

• No neurilemma or endoneurium

• Oligodendrocytes myelinate several fibers

  • Insulation speeds up conduction

What is a myelin sheath?

Node of Ranvier - between Schwann cells

What is the relationship of unmyelinated axons to their supportive cells?

PNS → “unmyelinated” cells have one Schwann cell wrapped around

• Nerve fibers go through Schwann cells

• Small fibers bundle and go through single channel

What are the steps to nerve regeneration in the PNS?

1. Observe normal nerve fiber (at NMJ)

2. Cut nerve fiber → stops protein synthesis

3. Degeneration: distal fibers begin and local Schwann cells follow (soma swell, some neurons die

4. Early regeneration: regeneration tube (Schwann cells produce molecute for growth (cell-adhesion))

5. Late regeneration: guides growing tube to original damaged cells

6. Regenerated fiber: regrowth and connection with original fibers (ex. muscle)

Explain why a cell has an electrical charge difference (potential) across its membrane: Electrical potentials

• Concentration difference in charged particles

• Living cells are polarized

• Currents are created by NA+ and K+ pumps

Explain why a cell has an electrical charge difference (potential) across its membrane: Resting Membrane Potential

• RMP ~-90 mV

  • More negative inside than outside cell

• K+ ions are more influential

  • Permeable plasma membrane

  • ICF is negative (pulls Na+ inside cell)

  • Reaches equilibrium

• Na+ ions trickle in

  • Reduces voltage to ~-70 mv

• Na+-K+ pump is ~70% of ATP in nervous system

  • Signals disrupt it and must work to stabilize RMP

How does stimulation of a neuron cause a local electrical response in its
membrane?

Depolarization

• Neuron stimulation by chemical (pain, smell, etc.)

• Opens Na+ channel

  • Combats negativity inside cell

  • Plasma membrane changes toward zero

What are the 4 types of local potentials?

1. Graded - Depends on stimulus

2. Decremental - Weaken leaving point of origin

3. Reversible - Stop in stimulation, returns to RMP

4. Excitatory or Inhibitory - Important for information processing

Explain how local responses generate a nerve signal.

The response begins at a dendrite, spreads through the soma, travels down the axon, and ends at the synaptic knobs.

What are the 5 types of neurotransmitters and their functions?

1. Acetylcholine - regulates cardiac contractions, BP, peristalsis, and glandular secretions

2. GABA - reduces excitability by inhibiting nerve transmission

3. Glycine - antioxidant, anti-inflammatory

4. Aspartic acid - hormone production, release; normal nervous system function

5. Glutamic acid - protein formation

What are the 2 types of neuromodulators?

1. Monoamines

   • Catecholamines (epi, NE, and dopamine)

     - Motor control, cognition, memory, endocrine system modulation

   • Indolamines

     - Regulates serotonin and histamine

2. Neuropeptides

   • Analgesia; reward; food intake; metabolism, reproduction; social behaviors; learning; and memory

What are 4 ways the stimulation of a postsynaptic cell is stopped?

1. Excitatory or inhibitory

   • Depends on receptor of receiving cell (post synaptic neuron)

2. Cholinergic Synapse (Diffusion of Ach)

   • Acetylcholine (Ach) - excites muscle

   • Inhibits cardiac

3. Inhibitory GABA-ergic Synapse

   • CI- channel targeted

4. Andrenergic Synapse (G protein m

What are the characteristics of neural integration?

• Summation

  • Adding up postsynaptic potentials and responding in the “trigger zone”

• Facilitation

  • One neuron enhancing the next

• Inhibition

  • One neuron (presynaptic) suppresses the next

Explain how the nervous system translates complex information into a simple code

Neural coding - All information that is sent to the CNS and everything within the CNS is sent as action potentials

How does the CNS know what is what?

• Qualitative information (eg taste or hearing) depends upon which neurons fire.

Quantitative information depend on:

• Different neurons have different thresholds

Stronger stimuli causes a more rapid firing rate (6 action potentials per second vs. 600)

Explain how neurons work together in groups to process information and produce effective output

Neural pools consists of interneurons

How does memory work?

• Pathway through the brain

• Synapses are permanently fixed for life

  • Respond and modify due to experience

  • Created or deleted in 1-2 hours

  • Synaptic plasticity: ability to change

• Trained “muscle memory”

What are the three types of memory?

1. Immediate (Sensory)

2. Short-Term

3. Long-Term (emotional vs procedural)

Immediate (sensory) memory

• Able to retain for a few seconds

• Important for reading

Short-term memory

• Few seconds to hours

• Working memory

Long-term (emotional vs procedural)

• Can last up to a lifetime

• Limited amount

What causes us to forget things?

• When neural circuits cease to fire

• Necessary when retaining tons of information

What are the 4 functions of the spinal cord?

1. Conduction - bundles of fibers pass info up and down spinal cord

2. Neural Integration - neurons receive, process, and send out info

3. Locomotion - repetitive, coordinated actions of several muscle groups

4. Reflexes - involuntary responses to stimuli; involves brain, spinal cord, and peripheral nerves

What are the four regions of the spinal cord and the basis for their names?

1. Cervical

2. Thoracic

3. Lumbar

4. Sacral

What are the 2 enlargements of the cord and why the cord is wider at these points?

1. Cervical - rise to nerves of the upper limbs

2. Lumbar - issues nerves to the pelvic region and lower limbs

What is the Medullary Cone and the Cauda Equinae?

Medullary Cone - tapered tip of cord

Cauda Equinae - nerve roots resemble horse’s tail

Name the 3 spinal meninges, in order from superficial to deep.

1. Dura mater - collagenous membrane surrounded by epidural space filled with fat and blood vessels

2. Arachnoid mater - layers of simple squamous epithelium lining dura mater and loose mesh fibers filled with CSF (subarachnoid space)

3. Pia mater - delicate membrane adherent to spinal cord

What is gray matter? What are the horns and process associated with it?

Gray matter - butterfly shaped; neuron cell bodies with little myelin (info processing)

• 2 posterior (dorsal) horns - sensory

• Interneuron process - in cervical and lumbosacral enlargements

  • Motor control/sensation in limbs

• 2 anterior (ventral) horns - motor

• Lateral Horn - T2 → L1 of spinal cord

What is white matter?

White matter - Myelinated axons (info pathways)

• Surrounds gray matter

• Axons bundles ‘funiculus’

• Divided into smaller fiber compartments

  • Spinal tracts

What the 5 types of spinal tracts?

1. Ascending - carries info up spinal cord

2. Descending - conducts motor impulses down

3. Decussation - cross over from left to right, up or down

4. Contralateral - origin and destination on opposite sides

5. Ipsilateral - origin and destination on same side

What are the meanings of the first through third order neurons in ascending tract?

1st - detects stimulus; transmits to brain/spinal cord

2nd - continues to thalamus

3rd - carries to cerebral cortex

What is the difference between upper and lower motor neurons in the descending tracts?

Upper - neurosoma in cerebral cortex

Lower - axon in brain/spinal cord

What is a nerve and the structure?

A nerve is a bundle of nerve fibers (axons)

• Epineurium - covers nerves

• Perineurium - surrounds fascicle

• Endoneurium - separates individual nerve fibers

What is the structure of a ganglion?

Dorsal root ganglion - cluster of neuron cell bodies in nerves in the PNS; sensory cell bodies

How many spinal nerves are there? What is their relationship to the spinal cord?

31 pairs of spinal nerves (1st cervical above C1)

• Nerves exit at intervertebral foramen

What are the names and locations of the five nerve plexuses?

1. Cervical (neck), C1 to C5

2. Brachial (armpit), C5 to T1

3. Lumbar (lower back), L1 to L4

4. Sacral (pelvis), L4, L5, and S1 to S4

5. Coccygeal, S4, S5, and C0

What are dermatones?

How spinal nerves receive sensory input from a specific area of skin

What makes up the brachial plexus?

1. Musculocutaneous - mixed-skin of forearm/elbow joint

2. Axillary - mixed-skin of lateral shoulder and arm; shoulder joint

3. Radial - mixed-skin of posterior arm; forearm and wrist

4. Median - mixed-skin of lateral 2/3 of hand; tips of digits

5. Ulnar - mixed-skin of palmar and digits III-IV

What is the sciatic nerve?

Major nerve extending from the lower end of the sc down the back of the thigh

What are reflexes?

Quick, involuntary stereotyped reactions of glands or muscle to sensory stim; automatic

Rostral v Caudal

Rostral - toward forehead

Caudal - toward cord

What are the three principal divisions of the brain?

1. Cerebrum

2. Cerebellum

3. Brainstem

Gyri v Sulci

Gyri - folds

Sulci - grooves

Where is gray matter located?

• Neuron cell bodies, cell bodies, dendrites, and synapses

• Forms cortex over cerebrum and cerebellum

• Forms nuclei deep within brain

Where is white matter located?

• Bundles of axons

• Forms tracts that connect parts of brain

What are the germ layers of development?

1. Endoderm (innermost)

   • Gut lining

2. Mesoderm (middle)

   • Mesenchyme

     • Intramembranous Ossification

3. Ectoderm (outermost)

   • Development of nervous system

What happens at the 4th week of development (embryonic)?

Development of forebrain, midbrain, and hindbrain

What happens at 5th week of development (fully developed)?

• Forebrain divides

  • Telencephalon

    • Cerebral hemisphere develops

  • Diencephalon

    • Thalamus and hypothalamus

• Hindbrain divides

  • Metencephalon

    • Pons and cerebellum development

  • Myelencephalon

    • Medulla oblongata

What are the 3 meninges of the brain?

1. Dura mater - outermost, tough membrane

   • Forms dural venous sinuses draining blood from brain

   • Forms supportive structures

2. Arachnoid - in spinal cord

   • Subarachnoid and subdural spaces

3. Pia mater - in spinal cord

   • Subarachnoid and subdural spaces

What are the 3 ventricles of the brain, locations and the passages that connect them?

1. Lateral ventricles

   • Location: cerebral hemispheres

     • Interventricular foramen

       • Connects lateral and 3rd ventricles

2. Third ventricle

   • Location: single vertical space

     • Cerebral aqueduct

       • Allows flow of CSF from 3rd to 4th ventricle

3. Fourth ventricle

   • Protects from trauma

     • Central canal connects down and through spinal cord

What are ventricles lined with?

Ependymal cells that produce CSF

What is the choroid plexus? How is it connected to ependyma?

Spongy mass of blood vessels on the floor of each ventricle

Connected to ependyma:

• Ependyma - neuroglia (looks like cuboidal epithelial)

  • Lines ventricles and canals; covers choroid plexus

  • Produces CSF

What are the methods of flow, reabsorption, and the functions of the cerebrospinal fluid (CSF)?

• Flow:

  • Fills ventricles and subarachnoid space

    • Constantly reabsorbed

• Functions:

  • Buoyant - floats brain so it neutral

  • Protection - cushions from hitting skull

  • Chemical stability - rinses wastes

• Absorption:

  • Absorbed into venous sinus through arachnoid villi

What are the steps of flow of CSF?

1. CSF is secreted by choroid plexus in each lateral ventricle

2. CSF flows through interventricular foramina into 3rd ventricle

3. Choroid plexus in 3rd ventricle adds more CSF

4. CSF flows down cerebral aqueduct to 4th ventricle

5. Choroid plexus in 4th ventricle adds more CSF

6. CSF flows out two lateral apertures and one median aperture

7. CSF fills subarachnoid space and bathes external surfaces of brain and spinal cord

8. At arachnoid villi, CSF is reabsorbed into venous blood of dural venous sinuses

What is the significance of the brain barrier system?

• Receives 15% of blood supply

• Utilizes 20% of oxygen and glucose

Function of Medulla Oblongata

All nerves that connect the brain to the spinal cord pass through

Function of Cerebellar peduncles

Connects cerebellum to the pons and midbrain

Function and structures of the midbrain

• Connects the hindbrain and forebrain

  • Superior colliculi

    • Controls extrinsic eye muscles

    • Respond to visual stimulus

  • Inferior colliculi

    • Receives signals from inner ear to relay to the thalamus and other parts of the brain

Describe what the reticular formation is, the location and functions

Loose web of gray matter

• Runs vertically through the brain stem and upper spinal cord

Functions:

• Somatic motor control

• Cardiovascular control

• Pain modulation

• Sleep and consciousness

• Habituation

What are the functions of the cerebellum?

1. Evaluation of sensory input

   • Coordination and locomotor ability

   • Spatial perception

2. Timekeeping center

   • Predicting movement

3. Distinguish pitch and similar sounding words

4. Planning and scheduling

What are the 2 major components of the diencephalon and their functions?

1. Thalamus

   • Receives all sensory information going to the cerebral cortex

   • Relays signals from cerebellum to motor cortex

   • Emotional and memory

2. Hypothalamus

   • Hormone secretion

   • Autonomic NS control

   • Thermoregulation

   • Food and water intake

   • Sleep and circadian rhyths

   • Memory

   • Emotional behavior

Identify the five lobes of the cerebrum and their functions

1. Frontal

   • Thought

   • Memory

   • Mood

   • Motivation

2. Parietal

   • Taste

   • Somatic sensation

   • Sensory integration

   • Visual processing

3. Occipital

   • Visual awareness and processing

4. Temporal

   • Hearing

   • Smell

   • Emotion

   • Learning

5. Insula

   • Taste

   • Pain

   • Visceral sensation

   • Consciousness

What are the three types of tracts in cerebral white matter?

1. Projection tracts - extend vertically between higher and lower brain and sc

2. Commissural tracts - cross from one cerebral hem to another

3. Association tracts - connect different regions with the same hem

What are the 3 locations of cerebral gray matter?

1. Cerebral cortex

   • Stellate cells

   • Pyramidal cells

2. Pyramidal cells

3. Limbic system

What is the limbic system?

• Important system of emotions and control

• Directly connects higher and lower brain functions

What are the 3 main parts of basal nuclei?

1. Caudate nucleus

2. Putamen

3. Globus pallidus

What are the four types of brain waves in a EEG?

1. Alpha - awake bust resting, eyes closed, not concentrating

2. Beta - receiving sensory stim

3. Theta - drowsy or sleepy state

4. Delta — Deep state

What are the 4 stages of sleep?

1. 1-7 minutes

   • Drowsy, relaxed

2. 10-25 minutes

   • Light sleep, sleep spindles (neurons of thalamus and cerebral cortex interact)

3. 20 minutes after stage 1 (theta and delta waves)

4. Muscles are relaxed and vital signs are low

What brain region is involved with memory?

• Hippocampus of limbic system

What brain regions are involved with emotion?

• Prefrontal cortex

• Diencephalon

Discuss the functional differences between the right and left cerebral hemispheres

1. Right hemisphere - language comprehension and visuospatial tasks (artistic tasks) and control the left side of the body

2. Left hemisphere - control the right side of the body, educational and rational side of the brain.

   • language, logic, science, written, communications, numbers. skills, and reasoning.

List the 12 cranial nerves by name and their function

I - Olfactory nerve; sense of smell

II - Optic nerve; vision

III - Oculomotor nerve ; eye movement, opening of eyelid, constriction of pupil

IV - Trochlear nerve; eye movement

V - Trigeminal nerve; sensory to face and muscles of mastication

VI - Abducens nerve; provides eye movement

VII - Facial nerve;

• Motor - facial expressions; salivary glands and tear, nasal and palatine glands

• Sensory - taste on anterior 2/3’s of tongues

VIII - Vestibulocochlear nerve; provides hearing and sense of balance

IX - Glossopharyngeal nerve; swallowing, salivation, gagging, control of BP and respiration

X - Vagus nerve; swallowing, speech, regulation of viscera

XI - Accessory nerve; swallowing, head, neck and shoulder movement

XII - Hypoglossal nerve; tongue movements for speech, food manipulation, and swallowing

What are the functions of cranial nerves?

Send electrical signals between your brain, face, neck, torso

How does the autonomic and somatic nervous systems differ in form and function?

Somatic:

• Effectors: Skeletal muscle

• Cell body in CNS, thick, myelinated muscle extends in spinal nerve to skeletal muscle

Autonomic:

• Effectors

• Uses two-neuron chain of pre and post ganglionic neurons

How does the two divisions of the autonomic nervous system differ in general
function?

1. Sympathetic

   • Prepares body for physical activity: exercise, trauma, arousal, competition, anger, or fear

     • Increases heart rate, BP, air flow, blood glucose levels, etc.

     • Fight-orFlight

2. Parasympathetic

   • Calms body functions reducing energy expenditure and assists in bodily maintenance

     • Digestion and waste elimination

What is autonomic tone?

Balance between the two systems (sympathetic and parasympathetic) depending on needs

Identify the anatomical components and nerve pathways of the sympathetic and parasympathetic divisions.

Sympathetic

• Thoracolumbar division

• Short preganglionic fibers

• Preganglionic neurosomas in gray matter

  • Sympathetic chain of ganglia

• Abdominal aortic plexus

  • Celiac

  • Superior mesenteric

  • Inferior mesenteric

Sympathetic Chain Ganglia

1. Spinal nerve route - Some postganglionic fibers exit a ganglion by way of the gray ramus to target organ (sweat glands, arrector muscles, and blood vessels of the skin).

2. Sympathetic nerve route - Other nerves leave by way of sympathetic nerves that extend to the heart, lungs, esophagus, and thoracic blood vessels

3. Splanchnic nerve route - Some fibers that arise from spinal nerves T5 to T12 pass through the sympathetic ganglia without synapsing

Parasympathetic

• Craniosacral division

  • Arises from the brain and sacral regions of the spinal cord

  • Fibers travel in certain cranial and sacral nerves

• Origin of long preganglionic neurons

  • Midbrain, pons, and medulla

  • Sacral spinal cord segments S2 to S4

Discuss the relationship of the adrenal glands to the sympathetic nervous system.

1. Adrenal cortex (outer layer)

   • Secretes steroid hormones

2. Adrenal medulla (inner core)

   • Sympathetic ganglion

   • Consists of modified postganglionic neurons without dendrites or axons

Describe the enteric plexus of the digestive tract and explain its significance

Regulates esophagus, stomach, and intestinal motility and enzyme secretion.

Name the neurotransmitters employed at different synapses of the ANS

Acetylecholine released by parasympathetics

Norepinephrine released by sympathetics