Intro and Organization of the Human Nervous System

NSUOCO 2025

The nervous system is the body’s command center, it regulates your body’s system. What is it responsible for controlling?

• movements

• thoughts (emotions)

• automatic responses

• digestion

• breathing

• sexual development

How can you damage your nervous system?

trauma, disease, toxins and aging

What is the nervous system composed of?

neurons - they send signals to and from cells all over the body

How does the nervous system interpret information and controls the body’s response?

• moving limbs

• feeling sensations

Motor neurons are also called

efferent

What does the term afferent correlate with?

sensory neurons

What does the central nervous system consists of?

The brain and spinal cord

What does the terms dorsal and ventral refer to?

dorsal - back 🐬

ventral - front

Where is the longitudinal axis of the forebrain?

Where is the longitudinal axis of the brainstem and spinal cord?

"Longitudinal" means relating to length, so this axis goes from the front to the back of an object. 

its an imaginary line running through the middle of these structures

What are the anatomical sections we view the brain in?

Coronal (👑) aka frontal section

mid-sagittal aka medial section

horizontal section

The nerve lies outside the brain and spinal cord and what is it a compilation of?

hundred of thousands of axons with associated connective tissue and blood vessels

What is ganglia made of?

neuronal cell bodies located outside the brain and spinal cord

The enteric plexus is an extensive network of neurons that help regulate what? Where is it located?

the enteric plexus helps regulate the digestive system and it is located in the walls of the GI tract

What are dendrites and specialized cells that monitor changes in the internal or external environment?

sensory receptors

What is the CNS (central nervous system)?

the brain and spinal cord

What is the PNS (peripheral nervous system)?

consists of the somatic nervous system and autonomic nervous system which breaks down into the sympathetic, parasympathetic, and enteric nervous system

The entire CNS is encased in ______. The brain is within ______. The spinal cord is within a ________ in the ______.

The entire CNS is encased in bone.

The brain is within the cranium.

The spinal cord is within a canal in the vertebrae.

What surrounds the CNS?

CSF (cerebrospinal fluid) and the meninges.

How many cranial nerves do we have?

12 pairs of cranial nerves

How many spinal nerves?

31 pairs of spinal nerves

Label the picture with the following terms:

• brainstem

• spinal cord

• cerebellum

• medulla

• cerebrum

• midbrain

• pons

What are the 3 functions of the nervous system?

• sensory

• integrative

• motor

How does the sensory function perform?

receptors detect changes in internal and external body conditions

How does integrative functions work?

coordinates sensory information and makes decisions that are acted upon by using motor functions

How do motor functions perform?

effectors respond when they are stimulated by motor impulses coming from the CNS through the peripheral nerves

List the functions of the PNS (hint there’s 3).

–Carry sensory information from the periphery to the CNS

–Conveying motor commands from CNS to the muscles

–Regulate autonomic functions

more than _______ nerve cells run through the body.

100 billion

The PNS consists of cranial and spinal nerves that branch out from the brain and spinal cord to all parts of the body. How many pairs of cranial nerves are there and how many pairs of spinal nerves?

12; 31

What are the divisions of the PNS?

• somatic nervous system

• autonomic nervous system

• enteric nervous system

What is the somatic nervous system?

sensory- sends info from bodily sensor receptors to the CNS and also sends special senses (vision, hearing, taste, smell) to the CNS

motor- controls impulses from the CNS to skeletal muscles

• consciously controlled

• VOLUNTARY

IMPORTANT:

The somatic nervous system is ________.

voluntary

Special sensations examples

• vision

• olfaction

• tastes

• hearing

• equilibrium and position

General sensation include:

somatic sensations and visceral sensations. list some of each type.

somatic sensations

• locomotor

• touch

• temperature

• pain

• proprioception

visceral sensations

• dull pain

• distention

The autonomic nervous system is __________.

involuntary - can be done without conscious effort

Along with the endocrine system, the autonomic nervous system is concerned with the regulation of

visceral activities that aid in maintaining homeostasis and it innervates structures like the heart, smooth muscle and glands

The ANS is made up of sensory neurons which

sends info FROM autonomic sensory receptors to the CNS.

Where are sensory receptors located?

in visceral organs, such as the stomach and lungs

in the ANS, motor controls nerve impulses from CNS to

SMOOTH MUSCLES, cardiac muscles and glands

What are the divisions of the ANS (autonomic nervous system)?

Sympathetic

Parasympathetic

Sympathetic is ‘flight or fight’; what is also associated with it

•Emergency, Excitement, Embarrassment

•Increased heart rate

•Skeletal muscle blood vessels dilate

•Other blood vessels constrict

•Decreased GI activity

•“Fight or Flight”

•NE/epinephrine

Parasympathetic is ‘rest/digest’, associated with

SLUDD

Decreased heart rate

increased GI activity

acetylcholine

What is SLUDD?

Salivation

Lacrimation

Urination

Digestion

Diarrhea

What is the enteric nervous system?

“Brain of the Gut”

its involuntary and has sensory and motor functions

What are the sensory functions of the enteric system?

oversees chemical changes in the GI tract

What are the motor functions of the EntericNS?

• contraction of smooth muscles to propel food through the GI tract

• regulates secretions of tracts or organs

• regulates activity of GI tract endocrine cells

What is gray matter composed of?

collection of neuronal cell bodies, dendrites, unmyelinated axons, axon terminal and neuroglia within the CNS

Why is gray matter gray?

the color of gray matter is due to NISSL bodies and lack of myelin

(UNMYELINATED AND NISSL BODIES)

What is myelin?

a mix of proteins and lipids, helps conduct nerve signals and protect the axons

What is white matter composed of?

collections of myelinated axons in the CNS

Why is white matter white?

white coloration comes from the lipid material in the myelin sheath

What matter has more motor output?

gray matter

What is the function of white matter?

conducts, processes, communicates and sends nerve signals up and down the spinal cord through tracts

• also sends nerve signals through commissural fibers and associated fibers

What are the functions of gray matter?

speech, hearing, feelings, seeing and memory

controls of the muscles

40%

The edges of the cerebrum (cortex) is ______ matter, while the center (nucleus) is ______

gray matter; white matter

What is the diencephalon and cerebrum apart of?

The forebrain

How can you view the diencephalon?

it is only visible upon cutting the brain

What is the midbrain composed of?

only the midbrain

What is the hindbrain?

pons, medulla, and cerebellum

What encases the spinal cord?

the vertebral column

What are the meninges that surround the spinal cord?

dura, arachnoid, and pia mater (dap)

What are the 31 segments of the spinal cord divided into?

• 8 cervical,

• 12 thoracic,

• 5 lumbar,

• 5 sacral,

• 1 coccygeal

  *it begins at the bottom of the brain stem and is continuous with medulla

What is the appropriate exits of the spinal cord?

cauda equina; it ends at the lower border of the first lumbar vetebrae

What are the vertebrae numerical categories?

hint: there’s a total of 33

• 7 cervical

• 12 thoracic

• 5 lumbar

• 5 sacral (fused)

• 4 coccygeal (fused)

What is the difference between vertebrae (33) and spinal nerve (31) categories?

the cervical (7- vertebrae; 8 - spinal nerves)

and coccygeal (4 fused for vertebrae; and 1 for spinal nerves)

What is there to know about gray matter and white matter comparing cerebrum to spinal cord

in the cerebrum the gray matter surrounds white matter but in the spinal cord you have the exact opposite.

What does the spinal cord allow the body to do?

–Move

–Feel temperature, vibration, sharp and dull sensations

–Sense the position of your limbs

–Control blood pressure, heart rate, and body temperature

–Control bodily functions

–Receives messages from the brain when the body moves

–Sends messages to the brain so a person can feel sensations

What are the functions of the midbrain?

connects the forebrain and hindbrain

cerebral aqueduct

Where is the cerebral aqueduct and what does it do?

in the midbrain

allows for cerebrospinal fluid (CSF) to flow between the third ventricle and the fourth ventricle.

What is a spinal cord injury?

damage to any part of the spinal cord, including damage to the vertebrae, ligaments or disks of the spinal column

classified as complete of incomplete

What is a complete spinal injury?

all feeling and motor function are lost below the injury

What is an incomplete spinal injury?

retain some sensory or motor function below the injury

What are some traumatic vs nontraumatic spinal cord injuries?

traumatic

• blunt trauma

• gunshot/ knife wound

nontraumatic:

• arthritis

• cancer

• inflammation

• infections/ disk degeneration of the spine

What is quadriplegia?

paralysis of all four limbs

what is paraplegia?

paralysis of both lower limbs

signs and symptoms of spinal cord injuries?

–Loss of movement

–Loss or altered sensation, including the ability to feel heat, cold and touch

–Loss of bowel or bladder control

–Exaggerated reflex activities or spasms

–Changes in sexual function, sexual sensitivity and fertility

–Pain or an intense stinging sensation caused by damage to the nerve fibers in your spinal cord

–Difficulty breathing, coughing or clearing secretions from your lungs

Spinal cord injuries affect the nerve fibers passing through the injured area. What does an injury to the lumbar region affect?

it can affect your torso, legs, bowel and bladder control, and sexual function

What can a cervical injury affect?

it can affect your torso, legs, bowel and bladder control, and sexual function (same as lumbar) plus movements of your arms and ability to breathe

Spinal cord injury complications.

•Bladder control

•Bowel control

•Skin sensation

•Circulatory control

•Respiratory system

•Muscle tone

•Fitness and wellness

•Sexual health

•Pain

Depression

Who is at risk of spinal cord injuries?

men, between the ages of 16-30, also over 65

engage in risky behavior or already have a bone or joint disorder

Spinal nerve injuries and disc categories, what is the main problem?

degenerative disc gets brittle

bulging in the soft tissue moves further out and eventually becomes herniated

THE problem is the disc starts to push on the nerve leading to a bunch of symptoms like neuropathy, burning senstion

What is special about the sciatic nerve?

it supplies nearly all of the skin of the leg, muscles of the back of the thigh, and those of the leg and foot.

What is the sciatic nerve derived from?

spinal nerves L4 through S3

The anterior root of the spinal cord is composed of

motor (efferent) nerve fiber

What composes the posterior root of the spinal cord?

The posterior root of the spinal cord is composed of sensory nerve fibers which carry sensory information from the body to the central nervous system (CNS)

What are treatment options of intervertebral disk degeneration?

–Physical Therapy/Exercises

–Disc Fusion

–Disc Replacement

What does the term “slipped disc” refer to?

a herniated disk, ruptured disk, or prolapsed disk

in which portions of an abnormal, injured, or degenerated disk have protruded against adjacent nerve tissues

frequently happening the low back, but any disk can rupture, including those in the neck

Spinal taps go into what?

go into the subarachnoid space, which is between the arachnoid mater and the pia mater. 

Spinal block vs epidural

both types of anesthetics involving placement of needles in lower backs used for childbirth/ lower limb surgery

spinal block (thinner needle, in to the CSF, no catheter, last 1-2 hours)

epidural (catheter into epidural space)

What are some head injuries?

•Scalp bruising

•Scalp scrapes

•Skull fractures

What are some non-trauma brain injuries?

-Vascular- Stroke/ aneurysm

-Cancer

-Disease/infection

-Swelling/edema (benign increased intracranial pressure)