NMS Lecture 1 - Neurons + The Nervous System

Neuroscience

study of the nervous system

Main parts of the CNS

Brain and spinal cord

Main parts of the PNS

Nerves that serve the neck arms, trunk, legs, skeletal muscles and internal organs

Stretch reflex

muscle contraction in response to stretching within the muscle

Patellar-tendon stretch reflex steps (general)

1. Tap the patellar tendon which attaches to the quadriceps muscle
2. Quadriceps muscle stretches, making the muscle longer
3. Activation of nerve impulses in stretch receptors located in quad
4. Nerve impulses are sent back to the spinal cord along the sensory neuron
5. Jerk or swing of the foot forward

Withdrawal reflex

a spinal reflex that pulls a body part away from a source of pain

Components of the central nervous system

Spinal cord, cerebral cortex, cerebellum, brain stem

Spinal cord anatomy

Anatomically similar along entire extent

Components of the peripheral nervous system

Comprised of peripheral nerves (all other nerves except CNS)

2 types of cells in nervous system

neurons and glial cells

Neuron proportion

Only 10% of nerve cells, but occupy 50% of volume

3 types of neurons

1. Afferent neurons - information from periphery to CNS
2. Efferent neurons - information from CNS to periphery
3. Interneurons - Information between neurons

Do afferent/efferent neurons excite or inhibit

Excite (activate)

Afferent neuron excitation

Can stimulate efferent neurons or interneurons

Efferent neuron excitation

Receive input from afferent or interneurons, stimulate muscle

Do interneurons excite or inhibit

Can do both

Interneuron stimulation

Receive input from afferent or other interneurons, stimulate interneurons or efferent neurons

Where interneurons located

In the CNS only

Glia (glial cells)

Glue of the nervous system. Numerous but tiny

Types of glia

astrocytes, microglia, oligodendrocytes, schwann cells

Oligodendrocyte function

Make myelin sheath in the CNS

Schwann Cell function

Make myelin sheath in the PNS

Dorsal spinal cord

Towards the posterior

Ventral spinal cord

Towards the anterior

2 main components of spinal cord

Gray matter and white matter

Gray matter and white matter shape

Gray matter is a horn/butterfly, white matter surounds it

Mixed peripheral nerve

Contains both afferent and efferent fibers

Afferent neurons carry information from periphery to CNS via...

Dorsal roots

Efferent neurons carry information from CNS to periphery via...

Ventral roots

Reflex loop

Activation of a receptor activates an afferent fiber which enters through the dorsal root of the spinal cord. This activates an efferent fiber which leaves the spinal cord via a ventral root and activate a muscle

Myelin function

Coats axons of neurons and allows for quicker nerve impulse transmission

Why is white matter white

White matter neurons are myelinated

Why is gray matter gray

Contains interneurons and unmyelinated neurons

Stretch reflex in terms of neurons

1. Tendon tap of the patellar tendon results in stretching of the quadriceps muscle
2. → stretching activates stretch receptors which are connected to afferent neurons
3. → information is sent from the muscle back to the spinal cord through the afferent neuron indicating that the muscle has been stretched
4. → afferent neuron travels with efferent neurons in the mixed peripheral nerve until it gets just outside the spinal cord
5. → afferent neuron enters through the dorsal root of the spinal cord and contacts an efferent neuron of the ventral part of the cord (via a synapse)
6. → efferent neuron exits through the ventral root of the spinal cord
7. → efferent neuron travels via the mixed peripheral nerve to the quadriceps muscle and results in its contraction

Role of interneurons in stretch reflex

Interneuron inhibits the efferent neurons that stimulate the antagonist muscle (in this case, the hamstring)

Neuron components

Dendrites, cell body, axon hillock, axon, axon terminal

Dendrites

Branchlike structures that receive information

Cell body (soma)

Contains the nucleus, manufactures proteins

Axon hillock

Processes information from dendrites and generates impulse if there is enough input

Axon

Propagates nerve impulse from initial segment to axon terminals

Axon terminal

Contains neurotransmitters to release to the synapse

Flow of information in nervous system

From dendrites/cell bodies down to axon terminal

Synapse

Junction between presynaptic terminal and post synaptic dendrite

Presynaptic neuron

Neuron before the synapse (releases neurotransmitter)

Postsynaptic neuron

Neuron after the synapse (receive neurotransmitter)

Types of neuron morphologies

Bipolar, Pseudo-unipolar, Multipolar

What type of neuron is a sensory neuron

Pseudo-unipolar

Where is the cell body of a sensory neuron located

Dorsal root ganglion of spinal cord

Peripheral axon (sensory neuron)

extends from cell body to the muscle, acts like the dendrites

Central axon (sensory neuron)

from cell body into CNS and makes contact with other neurons

What two neurons does the afferent neuron attach to in the stretch reflex, and why?

1. Efferent neuron to activate the quadriceps muscle to contract
2. Interneuron to inhibit the antagonist muscle from contracting, the hamstring