Nervous System

Anatomy of a neuron

Some

Dendrites

Initial segment

Axon colateral

Axon

Axon terminal

initial segment of axon

Area of the axon having the lowest threshold for stimulation, so the action potentials begin at this point

Axon colateral

a branch of an axon from a single neuron

Can axons differentiate?

No, they are terminally differentiated cells

Amniotic cell

A cell that cannot divide

- neurons!

Nuclei

clusters of neuron cell bodies in CNS

Ganglia

clusters of cell bodies in the PNS

What kind of metabolic need to neurons have?

High metabolic need

Ratio of neurons to glia

1:1

Types of glial cells

astrocytes, microglia, oligodendrocytes/schwann cells, ependymal cells

Astrocytes

Provide structural and metabolic support for neurons.

Form blood brain barrier

Microglia

Act as phagocytes, eating damaged cells and bacteria, act as the brains immune system

Oligodendrocytes and Schwann cells

form myelin sheath

- Oligodendrocytes in CNS

- Schwann cells in PNS

Ependymal cells

produce cerebrospinal fluid

How are neurotransmitters and other materials transported from the soma to the axon terminal?

Transported on microtubule tracks by kinesins and dyneins

Kinesin

motor proteins in anterograde transport

- to periphery of cell

- towards POSITIVE end of microtubule

Dynein

motor proteins in retrograde transport

- to nucleus of cell

- towards NEGATIVE end of microtubules

Classes of neurons

afferent, efferent, interneurons

Interneurons

Central nervous system neurons that internally communicate and intervene between the sensory inputs and motor outputs

Afferent neurons

Nerve cells that carry impulses towards the central nervous system from the PNS

- "sensory neurons"

Efferent neurons

Nerve cells that conduct impulses away from the central nervous system to the PNS

- "motor neurons"

Divisions of the PNS

Afferent and efferent

Divisions of afferent PNS

somatic sensory, visceral sensory, special sensory

somatic sensory division

carries signals from receptors in the skin, muscles, bones, and joints

- helps us sense touch, pain, temperature, vibration, etc

Visceral sensory division

carries signals from the viscera (heart, lungs, stomach, and urinary bladder)

- organ senses

Special sensory division

vision, hearing, taste, smell, balance

Divisions of the efferent PNS

somatic and autonomic

somatic motor division

carries signals to skeletal muscles

Divisions of autonomic nervous system

sympathetic, parasympathetic, enteric

Brain anatomy

Brain Lobes

-Frontal

-Parietal

-Temporal

-Occipital

Cerebellum

Brain stem

Frontal lobe function

involved in motor function, problem solving, memory, judgment, impulse control

Parietal lobe function

somatosensation and spatial processing

Temporal lobe function

Hearing, memory, language comprehension.

Occipital lobe function

visual processing

Cerebellum function

Balance and coordination

Parts of the brainstem

midbrain, pons, medulla oblongata, reticular formation

Forebrain

largest part of the brain, containing the cerebral cortex and the diencephalon

Diencephalon

thalamus and hypothalamus

Motor cortex

an area at the rear of the frontal lobes that controls voluntary movements

Somatosensory cortex

area at the front of the parietal lobes that registers and processes body touch and movement sensations

Hypothalamus

Master coordinator of the nervous and endocrine systems, responsible for controlling eating, drinking, reproduction, etc

Brainstem function

responsible for automatic survival functions

- all nerve fibers that relay signals go through the brainstem!

reticular formation function

• essential for life

• recieves and integrates information from across entire CNS

• regulates breathing, sleep, attention, circulation, movement

Integrating centers

neuron clusters in the brainstem that control GI, respiration, cardiovascular function, and more

What protects the spinal cord?

The vertebral column (spine)

What part of the spinal cord recieves incoming senory information?

The posterior (dorsal) horn.

What part of the spinal cord sends out motor signals?

The anterior (ventral) horn.

Fiber tracts

in the spinal cord that transmit signals between different regions of the central nervous system.

• run longitudinally through spinal cord

How many total nerve pairs are there in the PNS?

• 43 total

• 12 pairs of cranial nerves

• 31 pairs of spinal nerves

  • cervical

  • thoracic

  • lumbar

  • sacral

  • coccygeal

How many cervical nerves are there?

8

How many thoracic nerves are there?

12

How many lumbar nerves are there?

5

How many sacral nerves are there?

5

How many coccygeal nerves are there?

1

Function of cervical nerves

Control muscles and glands. Receive sensory input from head, neck, shoulders, arms hands

Function of thoracic nerves

Associated with chest and upper abdomen

Function of lumbar nerves

Associated with lower abdomen, hips, and legs

Function of sacral nerves

Associated with lower digestive tract and genitals

Are spinal nerves afferent or efferent?

Both!

Function of cranial nerves

special sensory function, balance, motor function of head, neck, facial muscles

Are cranial nerves afferent or efferent?

Some are purely afferent, some are purely efferent. Most are both.

Structure of somatic neurons

SINGLE neuron between CNS and skeletal muscles

Are somatic neurons inhibitory or excitatory?

Excitatory

Structure of autonomic neurons

Two neuron chain between CNS and affector organ/gland

What do autonomic neurons innervate?

smooth muscle, cardiac muscle, glands, GI organs

• NO SKELETAL MUSCLE

Are autonomic neurons excitatory or inhibitory?

Either or

Where do sympathetic neurons originate from?

Thoracolumbar region

Sympathetic neuron structure

Short pre-ganglionic axon and long post-ganglionic axons

What neurotransmitter(s) do sympathetic neurons use?

Acetylcholine for pre-ganglionic synapses

Epinephrine/norepinephrine for post-ganglionic synapses

Where do parasympathetic neurons originate from?

Craniosacral region

Parasympathetic neuron structure

Long pre-ganglionic axons, short post-ganglionic axons

What neurotransmitter(s) do parasympathetic neurons use?

Acetylcholine used for both pre- and post-ganglionic synapses

Structure of adrenal medulla

A set sympathetic post-ganglionic neurons

What does the adrenal medulla release?

Catecholamines

• 80% epinephrine

• 20% norepinephrine

Relationship between sympathetic and parasympathetic nervous systems

Antagonistic—never activated together!

Physical support structures for the CNS

cranium, meninges, CSF

Meninges

Series of membranes between the brain and skull that protect the brain, blood vessels, contain CSF, and form partitions

What are the meninge layers?

1. Dura Mater

2. Arachnoid Mater

3. Pia Mater

Dura Mater

Outermost layer of meninges

Arachnoid mater

2nd layers in the meninges.

• Subarachnoid space is filled with CSF and houses the largest blood vessels that supply the brain

Pia mater

The meninge layer closest to the brain

• clings to the brain EXTREMELY tightly

• most delicate

• contains a network of blood vessels

Cerebrospinal fluid

Extracellular fluid of the CNS that provides cushioning and maintains a stable a optimal environment

Where is CSF made?

In the choroid plexus by ependymal cells

Where is CSF found?

Circulates through the subarachnoid space and the ventricles

How much volume of CSF do we have in our body?

~125-150 mL

Recycling of CSF

CSF is reabsorbed by arachnoid villi. CSF is recycled 3 times a day!

Blood Brain Barrier

A layer formed of impermeable brain capillaries, thick surrounding basal lamina, and astrocytes which helps maintain a stable brain environment

Permeability of BBB capillaries

Most impermeable capillaries in the entire body

• ONLY lipid-soluble compounds can easily cross the BBB

What factors affect electrostatic force strength?

Quantity of charge and distance between charges

• Coloumb’s law

Resting membrane potential

Charge formed by the separation of ions across a membrane

Why do different cells have different resting membrane potentials?

It comes down to differences in membrane permeability!

RMP for neurons

-70 mV

Concentration of Na+ intracellularly vs extracellularly

Na+ higher extracellularly

Concentration of K+ intracellularly vs extracellularly

K+ higher intracellularly

Concentration of Ca2+ intracellularly vs extracellularly

Ca2+ higher extracellularly

How to membrane potentials change?

Movement of ions across the membrane

Nernst Equation

Tells us what the membrane potential would be if the membrane was ONLY permeable to the ion of interest

Goldman-Hodgkins-Katz equation

Allows us to calculate RMP by looking at individual ion contribution

What establishes the RMP?

Sodium-potassium ATPase

• 3 Na+ out, 2 K+ in

• Uses ATP

Depolarization

moving from RMP to more positive