Lecture 1: Basic Nervous System

Neuro-anatomical Overview and Basic Definitions

What does a typical neuron have?

• cell body

  • nucleus

• dendrites

• axons

• is multipolar

  • having several axons and dendrites

function of dendrites

receives most of the cells inputs

function of axons

carries most of the cells outputs

What are the two main types of neural transmission (2 ways neurons talk to each other)?

Chemical synapses and electrical synapses

In chemical synapses, a type of neural transmission, where are neurotransmitters stored before release?

In synaptic vesicles in the pre-synaptic terminal

In chemical synapses, a type of neural transmission, where do neurotransmitters bind after being released?

Neurotransmitter receptors on the post-synaptic neuron.

What are the two possible effects of neurotransmitter binding?

Excitation or inhibition of the post-synaptic neuron

How do neurons communicate in electrical synapses, a type of neural transmission?

Through electrical coupling via specialized junctions (gap junctions).

Which type of synapse is faster?

electrical synapses

In the CNS (brain + SC), which cells produce the myelin sheath?

Oligodendrocytes

• “COPS”

In the PNS, which cells produce the myelin sheath?

Schwann cells

• “COPS”

What are the gaps between myelin sheath on a neuron’s axon called, and what is special about them?

Nodes of Ranvier

• they contain voltage-gated ion channels which is important for regenerating the electrical signal along the axon

The axon is exposed at the nodes of ranvier, allowing …

the signal to "jump" from one node to the next, speeding up the transmission of nerve impulses along the axon

what structure is compromised in those with MS and why?

nodes of ranvier; problems with transmission signals

What is saltatory conduction?

The process of electrical impulses jumping from one Node of Ranvier to the next

Myelin sheath function

• insulates nerve fibers

  • It wraps around nerve fibers (axons) to protect them. 

• speed up nerve impulses

  • It helps electrical signals travel quickly and efficiently along the nerve. 

what is the function of non-neural support cells?

they provide support, protection, and nourishment to neurons. They also help maintain the environment necessary for neurons to function properly. 

examples of non-neural support cells in the CNS

• astrocytes

• oligodendrocytes

• microglia

• ependymal cells

examples of non-neural support cells in the CNS

• schwann cells

• satellite cells

function of astrocytes

Maintain the blood-brain barrier, provide nutrients to neurons, and support the repair of nervous tissue. 

• regulates blood flow, assists with homeostasis, uptake of neural transmitters and helps to protect the blood-brain barrier

function of oligodendrocytes

Produce myelin, which insulates axons

• has less branches than astrocytes

• “nerve glue”

function of microglia

Acts as the immune cells in the brain, cleaning up waste and fighting infections

function of ependymal cells

Lines the brain's ventricles and SC, helping produce and circulate cerebrospinal fluid

function of schwann cells

Produce myelin for axons, similar to oligodendrocytes in the CNS

• some aren’t myelinated

function of satellite cells

Surround and support neuron cell bodies, regulating their environment 

What are the different types of nerves cells? 

• Motor neurons in spinal cord = functions in SC  

• Alpha motor neurons = “lower motor neuron” contributes to skeletal muscle contraction  

• Pseudo unipolar sensory neuron = sensory function

• Dorsal root ganglion sensory neurons = sensory function

• Cerebellar Purkinje neurons = functions in cerebellum  

• Pyramidal cells = functions in medulla? At pyramidal tract

non-neural support cells, AKA…

glial cells, neuroglia

• cells in the nervous system that do not transmit electrical signals like neurons do

why is it a good thing to have more dendrites than axons?

It allows the neuron to receive input from a greater number of other neurons. This increased input capacity is crucial for integrating information from various sources

what structure can DM type 2 damage and what occurs because of it?

• Schwann cells

• as a result, negatively impacts their sensation in a stocking glove pattern. Because the part that's supposed to speed up info moving along is now damaged

Alpha motor Neuron

Large, multipolar lower motor neuron in the brain stem + SC

smooth ER function

create/store lipids and steroids

rough ER function

helps synthesize proteins

Pseudounipolar sensory neurons

• has no dendrites

• is part of the PNS

• carries info about touch, vibration, proprioception, pain & temp

dorsal root ganglion sensory neuron

is the primary sensory neuron of pain and touch

pyramidal cells are

excitation cells in CST but are associated with primary motor pathway

purkinje fibers function

• receives input from brainstem & spinal cord and gives info to the deep cerebellar nuclei

• distinct in feature because of their massive branches

during an action potential, at resting state….

the membrane potential is at -70 mA and the inside is more negative than the outside, this is when the cell is polarized

what happens during depolarization stage of action potential?

the axon receives some signal, then once it reaches -55mA, the sodium (Na+) channel opens and sodium ions enter and makes the voltage rise.

Now the inside of the cells is more positive than the outside and the voltage increase (steps 2 to 3 on chart)

when does an action potential actually occur?

If enough Na+ enters and the charge reaches a certain threshold, an action potential (electrical impulse) is triggered.

The impulse travels down the axon. 

What happens during Repolarization phase of action potential?

• Potassium (K+) channels open, allowing K+ ions to flow out of the cell. 

• This restores the negative charge inside the cell. 

• (steps 3 to hyper-polarization on chart)

what is the hyperpolarization phase of an action potential?

Sometimes, too many K+ ions leave the cell, making the inside even more negative than the resting state. 

After repolarization phase, what happens?

return to resting state

• The sodium-potassium pump works to restore the original balance of Na+ and K+ ions, returning the cell to its resting state. 

• The cell is now ready to fire another action potential. 

What are neurotransmitters?

Chemical messengers that carry signals across the synapse
(the gap between two neurons)

What is an EPSP?

An excitatory postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential

How do EPSPs make a neuron more likely to fire?

By opening channels that let positive ions (like Na⁺) in, causing depolarization

What is an IPSP?

An inhibitory postsynaptic potential that makes the postsynaptic neuron less likely to fire an action potential

How do IPSPs make a neuron less likely to fire?

By opening channels that let negative ions (like Cl⁻) in or positive ions (like K⁺) out, causing hyperpolarization.

What is neuromodulation?

A slower process where neuromodulators change how neurons respond to signals, boosting or reducing activity

Give examples of neuromodulators.

Dopamine, serotonin, acetylcholine, peptides

How is neuromodulation different from regular neurotransmitter action?

Neurotransmitters send quick, specific signals; neuromodulators adjust the strength or responsiveness of those signals.

Main CNS neurotransmitter producing EPSPs

Glutamate

Excess glutamate can cause…

excitotoxicity, leading to neuron damage

what conditions might we see excess glutamate? how may patients present?

stroke or TBI; may experience muscle spasticity or increased tone

Main CNS neurotransmitter producing IPSPs.

GABA

Low levels of GABA can result…

in anxiety, muscle tension, or seizures.

In PT, low levels of GABA may present as….

muscle hyperactivity or difficulty relaxing muscles. 

CNS neuromodulators and their roles

Dopamine, serotonin, peptides (e.g., substance P) → adjust circuit responsiveness rather than fast EPSP/IPSP signaling

What disorder is associate with low levels of dopamine (CNS neuromodulator)? what can it lead to?

Parkinson’s Disease; tremors, stiffness, and slow movement (bradykinesia)

What can Serotonin (CNS neuromodulator) Imbalance contribute to?

mood disorders and can affect pain perception

Elevated Peptides, like substance P (CNS neuromodulator), can cause…

increased pain signals which is seen in chronic pain conditions

Primary PNS neurotransmitter at the neuromuscular junction (NMJ)

acetylcholine

Acetylcholine in the PNS is crucial for…

muscle activation

PNS Ach dysfunction/Issues with NMJ is associated to what disorder and may cause what?

Myasthenia Gravis (autoimmune); muscle weakness or paralysis

Main ANS neurotransmitters

Acetylcholine (ACh) and norepinephrine (NE)

Functional role of ACh in ANS

Major transmitter for parasympathetic (“rest and digest”) pathways; regulates heart rate, digestion, and other involuntary functions

what conditions can occur due to dysregulation of Ach in the ANS?

bradycardia (slow heart rate) or digestive issues
- parasympathetic abnormalities

Functional role of Norepinephrine (NE) in ANS

Major neurotransmitter for sympathetic (“fight or flight”) pathway/response

Imbalance of NE in ANS can result in which symptoms?

High blood pressure, anxiety, or excessive sweating, which can affect physical therapy outcomes

What is gray matter composed of?

Neuron cell bodies (somata)

What is white matter composed of?

Myelinated axons that interconnect different areas of the CNS

Where is gray matter primarily found in the brain?

On the surface (cerebral and cerebellar cortices), with some deep structures like the basal ganglia.

• outside

Where is white matter located in the brain?

Deep to the gray matter of the cortex and surrounding deep gray matter structures. (found in cortices)

• inside

How is gray matter arranged in the spinal cord?

Deep/Inside, forming a butterfly or H shape.

How is white matter arranged in the spinal cord?

External, surrounding the deep gray matter

Name some terms used for collections of axons (white matter)

Tract, funiculus, fasciculus, bundle, column, stria, projection, lemniscus.

Can axon bundles carry signals in one or both directions?

Both

Example of a one-way axon bundle.

Fasciculus gracilis → carries signals one way (from lower extremities to brain)

• sends signals up the chain

• part of the DCML pathway

Example of a two-way axon bundle.

Medial Forebrain Bundle → carries signals in both directions

What is the functional relevance of the fasciculus gracilis?

Transmits lower extremity sensory information to the brain

What is the conus medullaris?

The tapered end of the spinal cord, usually at the L1-L2 vertebral level

Function of the conus medullaris?

Marks the end of the spinal cord; site where nerve roots for the lower body branch out

Effects of a conus medullaris injury?

Symptoms in both legs, bladder, and bowel, often with sudden weakness or paralysis

• sudden onset

What is the cauda equina?

A bundle of spinal nerve roots extending below the conus medullaris, resembling a horse’s tail

• the group of nerve roots that continue down the spinal canal until they exit

Function of the cauda equina?

Controls sensation and movement of the lower limbs and pelvic organs

Effects of a cauda equina injury?

Gradual onset of weakness, numbness, and bladder/bowel dysfunction, usually affecting the lower body.

axons in white matter…

travel greater distances (spinal tracts)

axons in gray matter…

responsible for most local synaptic communication between neurons

Cerebrum & brain location

above cerebellum

brainstem is made up of…

midbrain, pons, and medulla

• functions in modulation of cortical input/output

• descending info from the cortex decussates here

cranial nerve nuclei are…

in the brain stem = Bulbar system

afferent

toward a structure, typically sensory

efferent

away from a structure, typically moto

CS Peripheral Nerves C1-C7 exit Spinal Cord ... the vertebral segment

above

CS Peripheral Nerves C8 exit Spinal Cord ... C7 vertebra

below

T1-S5 Peripheral Nerves exit Spinal Cord ... the vertebral segment

below

Spinal Cord ends at ...

L1-L2 vertebral level

spinal nerves are…

mixed nerves that carry both sensory and motor information.

Ascending sensory pathway

• First-order sensory neuron enters the dorsal horn of the spinal cord.

• Carries information from the body to the CNS (touch, pain, temperature, proprioception).

Descending motor pathway

• Lower motor neuron exits from the ventral horn of the spinal cord.

• Carries commands from the CNS to muscles, producing movement

Autonomic Nervous System

- controls automatic functions (HR, Peristalsis, Sweating, Smooth muscle contraction)

- Peripheral control with Supra-Spinal Modulation