Anatomy & Physiology 12 Name:

Ms. Hansen

The NERVOUS SYSTEM

12.1 Nervous Tissue

Function:

Consists of:

Central Nervous System (CNS):

Peripheral Nervous System (PNS):

The Nervous system contains 2 types of cells: Neurons and Neuroglia

Neurons between parts of the

nervous system

Neuroglial cells

, maintain homeostasis and form

Neurons have 3 parts; dendrite, cell body, axon

Dendrite - carries the nerve impulse

Cell body - contains the of the cell which maintains cell function

Axon - carries the action potential the cell body towards another

or an

Sensory neuron

May have specialized endings called which detect changes in the

environment and carry the message to the CNS.

Interneuron

Receives messages from other interneurons,

received and communicate with

Motor neuron

Carry the message from the to an (muscle, organ or glands)

Myelin Sheath

Some axons are covered in a protective myelin sheath to

and aid in nerve regeneration.

Myelin is a type of lipid found in the membranes of

(neuroglia in the PNS) or (neuroglia in the CNS)

Nodes of Ranvier: gaps between Myelin Sheath (allows for ~200m/s transmission) (without:

5m/s) “Saltatory conduction”

Tracts: bundles of myelinated axons in CNS (white matter)

Nerves: bundles of myelinated axons in PNS

12.2 Transmission of nerve impulses

A nerve impulse is also called an

When the neuron is not firing, it has a of ~ mV.

Action potential

A rapid change in polarity across an axonal membrane

As the action potential moves through the neuron, the same

three steps occur;

1. Depolarization

open

Sodium ions move

Sodium gates close

2. Repolarization

open

Potassium ion diffuse of the neuron

Potassium gates close

3. Refractory period

The ions are on the wrong side of the membrane

The restores the previous ion

distribution by moving 3 sodium out and 2 potassium in.

Anatomy & Physiology 12 Name:

Ms. Hansen

The Synapse

A synapse is a region where the axon of one neuron is in

to the cell body or dendrite of another

are used to carry the action potential across

the synaptic cleft

Process of transmission

1. The nerve impulse reaches and

cause gates to open (instead of Na+)

2. Calcium ions diffuse into the neuron and interact with the contractile

proteins that causes the (containing the neurotransmitters) to with

the presynaptic membrane

3. The neurotransmitters are released into the synaptic cleft ( ).

4. The neurotransmitters across the synaptic cleft to (on Na+

channels) on the post synaptic membrane (dendrite or cell body of the next neuron)

5. Depending on the type of NT and receptor, this alters the potential of the post synaptic membrane

either in an or manner.

Excitatory signals have a depolarizing effect causing the membrane potential to move

closer to threshold. Inhibitory signals have the opposite effect

6. The neurotransmitters are then either by the presynaptic membrane or

by enzymes in the synaptic cleft

Neurotransmitters

There are at least 25 different NT’s identified

Examples: Acetylcholine (ACh) and Norepinephrine (NE)

Specific enzymes are present in the post synaptic membrane to break down these NT’s

o i.e. Acetylecholinesterase (AChE)

Synaptic integration

A neuron has many synapses. It also has a threshold that must be

reached in order for it to fire.

Excitatory NTs cause the neuron to get closer to its threshold. (open

Na+ channels)

Inhibitory NTs cause the neuron to get further away from the threshold

(may open K+ or Cl- channels K+ out or Cl- in = hyperpolarization)

There could be up to 200 synapses on a post synaptic neuron. Each

synapse may be contributing excitatory or inhibitory NTs.

The combination of excitatory and inhibitory NTs must be enough to

reach the threshold

Size of the action potential

The size of the action potential produced in a neuron Is

. You can tell a strong

stimulus (knife cut) from a weaker stimulus (pin prick) in two

ways

o for the

strong stimulus

o The neurons will fire for the

stronger stimulus

Synapses in drugs (research)

Anatomy & Physiology 12 Name:

Ms. Hansen

The Central nervous system

Composed of the and

Protected by

o Bone: Scull and vertebrae

o 3 tough layers of membrane

o

found between the meninges, in the central canal and in

the ventricles of the brain

cushions the brain and the spinal cord

o Spinal cord leaves skull through

Spinal cord

Structure:

Grey matter:

White matter (myelinated) : bundled together in

o Ascending tracts

o Descending tracts

Function:

Grey matter:

o Ex: Reflex arc

White matter:

o Ex: Receptors in skin send message through sensory neurons to spinal cord, up ascending

tracts to brain, brain sends message down descending tracts in spinal cord then through

motor neurons to effector.

The Brain

4 Main parts

1.

2.

3.

4.

Cerebrum

Largest part of the brain

The outer surface of grey matter is called the . This area accounts for

and

Its divided into the left and right hemispheres by the .

Each hemisphere has 4 lobes; the Frontal, Parietal, Occipital and Temporal lobes.

Cerebral cortex

Somatosensory cortex receives information from your body

Motor cortex sends information out

Frontal lobe

Primary motor cortex control voluntary

Association (premotor) areas organize complex motor activities

Processing center: Prefrontal area allows humans to

and formulate ,

Broca’s area is associated in refining grammar/

Parietal lobe

Primary somatosensory cortex

(touch, temperature, pain)

Somatosensory association area analyzes information from

the skin and muscles

Occipital lobe

Dedicated to

Visual association area compares new images with old images to

determine if there are any relationships

Temporal lobe

Primary auditory area receives information from

Auditory association area is used to match new sounds with

“remembered” sounds

Processing center: Wernicke’s area: helps understand

Receives information from

Phineas Gage

Cerebellum

Receives sensory input from and

to control

and works with cerebral (motor) cortex to ensure

smooth complex muscle movement

Maintains posture

Diencephalon: Thalamus, Hypothalamus and Pineal gland

The receives input from the visual,

auditory, taste and somatosensory areas (PNS) and send it

to the appropriate areas of the cerebrum.

The Thalamus is also involved in higher mental functions

such as memory and emotions

The Hypothalamus regulates , ,

, ,

and .

The Hypothalamus also produces (via neurosecretory cells) and controls

the (links nervous and endocrine systems)

Pineal gland

Secretes hormone melatonin to regulate your body’s daily rhythms (sleep and wake cycles)

The Brain Stem

, ,

Midbrain

• between the Cerebrum and the Spinal cord or Cerebellum

• Has reflex/processing centers for certain visual and auditory responses

Pons

The Pons contain that travel from the to the rest of

the

Works with the medulla oblongata to

Medulla oblongata

Contain many reflex centers for controlling

o Heartbeat

o Respiration

o Vasoconstriction

o Reflex centers for

Coughing

Swallowing

Vomiting

Sneezing

hiccuping

corpus callosum

• A bridge of white matter which passes information

between the right and left cerebral hemispheres

RAS (reticular activating system)

Network of nuclei and nerve fibers within

the brain stem

Receives sensory information and relays it

through the thalamus into the cerebrum.

Can be “awaken” with a sudden stimulus or

deactivated by turning off visual and

auditory stimuli

Can filter out unnecessary stimuli

Injury to RAS can cause COMAs

Limbic system

• The two main structures within the Limbic system are the Hippocampus and the Amygdala.

• Function in learning and memory

• The Amygdala also functions in responding to and displaying anger and fear

• Prompts release of adrenaline

Anatomy & Physiology 12 Name:

Ms. Hansen

The Peripheral Nervous System

Structurally the PNS consists of a

that project out of the brain and spinal cord pairs cranial

nerves (sensory, motor or mixed nerves) pairs spinal

nerves (all mixed)

Cranial nerves: Cranial nerves serve the

Spinal nerves: Two short branches ( )

leave the spinal cord and join as one

Somatic and Autonomic NS

Functionally, the PNS can be broken down into the

(voluntary) and (involuntary) nervous systems

Somatic NS

Serves the .

Takes information and

sends to

some actions are

Reflex arc: Somatic system

Receptor detects

Stimulus passes through sensory neuron into spinal cord

Axon passes impulse to a number of

One of the interneurons within the grey matter passes the impulse on

to the , another one passes the impulse up

the spinal cord to the

Autonomic Nervous System

Functions automatically

Innervate the

Each signal is passed through to an effector (synapse in a ganglion)

Sympathetic division

Nerves leave the middle (thoracic-lumbar area) part of the spinal

cord

The motor neuron is while

the neuron is .

Used in emergency situations

response

↑ heart rate, dilates bronchi, inhibits digestion

The NT released is and (NE)

Hormones are also involved: is

stimulated (by a neuron) to release

(adrenaline) and

Parasympathetic division

Nerves leave the cranium or the sacral area of the spinal

cord

The motor neuron is

while the motor neuron is .

In fact the ganglion often lies on top of the organ

Keeps or returns the organs to a state

Promotes

after a stressful situation, and caused the pupil to contract

“housekeeping”

The NT is