3: Nervous System

What does the nervous system consist of?

• Brain

• Spinal Cord

• Nerves

What is the central nervous system?

The brain and the spinal cord

What is the peripheral nervous system?

The nerves of the body

What are the 2 functions of the nervous system?

• Controls and integrates bodily activity

• Reacts to constant changes in external and internal environments

What are neurons?

• The basic unit of the nervous system

• Transmit electrical impulses to one another to communicate information

What are the 2 kinds of cells in the nervous system? Provide an example.

• Neurons (motor and sensory)

• Neuroglia (Oligodendrocytes and Schwann cells)

What are the 2 kinds of neurons?

1. Multipolar motor neuron

2. Pseudounipolar sensory neuron

What is a multipolar motor neuron?

A motor neuron with 2 poles: the cell body to the periphery

• Send information from the CNS to the PNS

What is a pseudounipolar sensory neuron?

Has the cell body in the middle, with one end recieving information in the periphery, pushed into the cell body, and sent to the central nervous system.

What are neuroglia?

• Non-neuronal, non-ecitable cells

• Provide support for neurons (structural, nourishment, insulation, pathogen clearance)

What are 2 examples of neuroglia?

1. Oligodendrocytes

2. Schwann cells

What is the role of oligodendrocytes?

Produce myelin sheath for the central nervous system

What is the role of Schwann cells?

Produces myelin sheath for the peripheral nervous system

What are the components of a multipolar motor neuron?

• Cell body

• Dendrites

• Axon hillock

• Axon

• Axon terminals

• Myelin sheath and Nodes of Ranvier

Flows from proximal to distal

What are the components of a pseudounipolar sensory neuron?

• Cell body

• Central process of the axon (towards the CNS)

• Peripheral process of the axon (back from the PNS)

• Dendrites

• Axon hillock

• Axon terminals

What is a ganglia?

A collection of cell bodies from multiple neurons within a nerve

How do oligodendrocytes work?

Forms several myelin sheaths around multiple axons in the CNS

How do Schwann cells work?

Forms one myelin sheath around one section of an axon in the PNS

What is multiple sclerosis?

A condition caused by the degradation of oligodendrocytes

What is Guillain-Barre syndrome?

A condition caused by the degradation of Schwann cells which may lead to weakness and paralysis

What is white and grey matter?

• White matter is the myelinated axons of neurons

• Grey matter is the dendrites and cell body

What is the difference between a myelinated and unmyelinated neuron?

• In an unmyelinated neuron, conduction is slower (0.5-2 m/s)

• In a myelinated neuron, conduction is faster (3-120 m/s)

Why is conduction faster in a myelinated neuron?

Because depolarization does not need to constantly occur along the axon, only at the Nodes of Ranvier

What happens at a neuronal synapse?

Where the axon terminals of a pre-synaptic neuron send a message to the dendrite of a post-synaptic neuron.

What are the 5 steps of a chemical synapse?

1. Nerve impulse arrives at axon terminal

2. Impulse opens calcium channels and calcium ions rush into presynaptic neuron

3. Calcium entering releases neurotransmitters into the synaptic cleft

4. Sodium channels on postsynaptic neuron open and sodium flows into postsynaptic neuron

5. New nerve impulse

What is a structural division?

Structures divided based on where they are and their role

What is a functional division?

Describes the pathways involved in a function

What are the 2 functional divisions of the nervous system?

1. Autonomic nervous system (ANS)

2. Somatic nervous system (SNS)

What are the 2 structural divisons of the nervous system?

1. Peripheral nervous system

2. Central nervous system

What is the autonomic nervous system?

Peripheral innervation to visceral organs and glands (involuntary)

What are the 2 divisions of the autonomic nervous system?

1. Sympathetic

2. Parasympathetic

What is the somatic nervous system?

Peripheral innervation to all other tissues (muscles, skin, etc.) —> voluntary

What is the parasympathetic nervous system?

“Feed and breed” or “rest and digest” system from the brain and sacral spine

What is the sympathetic nervous system?

'“Fight or flight or fright” system from the sympathetic trunk/chain

What are 3 components of the somatic nervous system?

1. Spinal nerve (messenger)

2. Muscle/myotome (motor)

3. Skin/dermatome (sensory)

What are the 4 lobes of the brain?

1. Frontal lobe

2. Parietal lobe

3. Occipital lobe

4. Temporal lobe

What is the function of the frontal lobe?

Motor and higher-order function

What is the function of the parietal lobe?

Sensory and sensory integration

What is the function of the occipital lobe?

Vision and visual processing

What is the function of the temporal lobe?

Auditory, smell, and memory processing

What are the 3 broad divisions of the brain?

1. Cerebrum

2. Cerebellum

3. Brainstem (midbrain, ponds, medulla)

What is the function of the cerebellum?

Motor coordination and some cognitive and emotional functions

What is the function of the midbrain?

Basal functions and pathways

What are the 5 divisions of the spinal cord?

1. Cervical

2. Thoracic

3. Lumbar

4. Sacral

5. Coccygeal

What are the different enlargements of the spinal cord?

• Cervical enlargement (for brachial plexus)

• Lumbar enlargement (for lumbosacral plexus)

What level does the spinal cord end at?

LI-LII

What are the components of spinal cord below the terminating point?

• Conus medularis

• Cauda equina

• Filum terminale

What are the 7 components of the spinal cord seen in a cross-section?

• Grey matter

• White matter

• Central canal (for cerebrospinal fluid)

• Posterior horn (sensory input)

• Anterior horn (motor input)

• Lateral horn (autonomic input)

• Spinal nerves

What are the 3 layers of spinal cord meninges?

• Dura mater

• Arachnoid mater

• Pia mater

Describe the dura mater.

• The very outer layer

• Thick outer layer

• Protects spinal cord

Describe the arachnoid mater.

• Spider-line middle layer

• Gives cerebrospinal fluid stability

Describe the pia mater.

• Tender inner layer

• Wrapped directly around the spinal cord

Describe the 2 components of the pia mater?

• Denticulate ligaments —> anchors spinal cord

• Cerebrospinal fluid (CSF) —> within subarachnoid space, provides support

What are the 3 spaces in the spinal cord meninges?

• Subarachnoid space

• Subdural space

• Epidural space

What are the applications of the spinal cord meninge spaces?

Freezing the lower limb with aneasthetic or drawing cerebrospinal fluid.

• Epidural (slower)

• Lumbar punture (faster)

What are the components of the spinal nerves?

• Posterior roots and rootlets (sensory)

• Anterior roots and rootlets (motor)

• Spinal nerve enters intervertebral foramen

• Splits to posterior and anterior ramus

What is the posterior ramus?

The sub-division of the spinal cord that sends motor AND sensory signals in the muscles and skin of the back.

What is the anterior ramus?

The sub-division of the spinal cord that sends motor AND sensory signals to all other muscles and the skin.

What are spinal plexuses?

Spinal nerves from different levels combine and seperate within plexuses to create peripheral nerves that carry fibers from multiple spinal levels

What is the sympathetic trunk?

Sympathetic neurons from the lateral horn at levels T1-L2 join together to carry sympathetic signals throughout the periphery

Where are the parasympathetic innervations located?

They are craniosacral (S2-S4)

What are the 4 cranial nerves of the parasympathetic system?

• CN III (oculomotor n.)

• CN VII (facial n.)

• CN IX (glossopharyngeal n.)

• CN X (vagus n.)

What are the 4 divisions of controls of the cranial nerves?

1. General somatic (skeletal muscle, skin)

2. General visceral (blood vessels, glands)

3. Special somatic (vision, hearing)

4. Special visceral (taste, smell)

What does the oculomotor nerve control?

Pupillary constriction through the sphincter pupillae muscle and dilator pupillae muscle

What 3 things does the facial nerve control?

• Production of tears (lacrimal gland)

• Production of saliva (submandibular glands)

• Production of mucus (nasal cavity and palate)

What does the glossopharyngeal nerve control?

Production of saliva (parotid gland) and sensory from the carotid sinus

What 3 things does the vagus nerve control?

• Bronchi and lungs

• Heart

• Esophagus, foregut, and midgut

What is homeostasis?

Automatic and unconscious processes that maintain a stable state in the body

What is the diencephalon?

• Thalamus

• Hypothalamus

Where is the main area that is responsible for maintaing homeostasis and how?

The hypothalamus —> recieves and integrates sensory information and generating a motor response

What is the pituitary gland?

An endocrine structure closely related to the hypothalamus that plays a large role in mood regulation

What kind of neurons does the somatic motor system use?

Multipolar motor neuron

What kind of neuron does the visceral motor system use?

Pseudounipolar neurons

What are the components of a parasympathetic neuron?

• Long presynaptic neuron (myelinated)

• Leads to parasympathetic ganglion

• Short post synaptic neuron (unmyelinated)

What are the components of a sympathetic neuron?

• Short presynaptic neuron (myelinated)

• Leads to sympathetic ganglion

• Long postsynaptic neuron (unmyelinated)

What are the impacts of the SNS and PSNS in your heart?

SNS: increased heart rate and contraction force

PSNS: lowered heart rate and contraction force

What are the impacts of the SNS and PSNS in your lungs?

SNS: bronchodilation, faster breath rate

PSNS: bronchoconstriction, slower breath rate

What are the impacts of the SNS and PSNS in your digestic system?

SNS: decreased digestive activity

PSNS: increased digestive activity

What are the impacts of the SNS and PSNS in your salivatory glands?

SNS: decreased saliva and tear production and excretion

PSNS: increased saliva and tear production and excretion

What are the impacts of the SNS and PSNS in your pupils?

SNS: pupillary dilation

PSNS: pupillary constriction

What are the impacts of the SNS and PSNS in your genitalia?

SNS: orgasm/ejactulation; decreased urinary function

PSNS: arousal/erection; increased urinary function

What are the impacts of the SNS only on your sweat glands and hair?

Sweat gland excretion and hair erection

What are the 4 components of the sympathetic trunk?

1. Right sympathetic trunk/chain

2. Left symapthetic trunk/chain

3. White rami communicantes

4. Grey rami communicantes

What is a white ramus communicans?

Where a neuron joins the sympathetic trunk

What is a grey ramus communicans?

Where a neuron is leaving the trunk

What spinal levels only have grey ramus communicans?

The spinal levels below and above the sympathetic trunk in which things are only exiting the trunk.

• C1-C8

• L3-Co

What is a sphlanchnic nerve?

A presynaptic nerve that leaves the sympathetic trunk without synapsing, and synapses at a different area with a more distal neuron

What is referred pain?

When pain is referred from a different area than the real origin due to periphery pain interpretation

What does craniosacral refer to?

How the parasympathetic nervous system has nerves coming from the brain as well as S2-S4 (sacral) spinal levels

How can we leverage the vagus nerve?

By controlling our breathing through the diaphragm and phrenic nerves.