The Nervous System

Neurons

The neuron is the functional unit of the nervous system. Humans have about 100 billion neurons in their brain alone!

While all are different in size and shape, all neurons have three main parts.

Dendrites receive information from another cell and transmit the message to the cell body.

The cell body contains the nucleus, mitochondria and other organelles typical of all eukaryotic cells.

The axon conducts messages away from the cell body.

Types of Neurons Three types of neurons occur. Sensory neurons carry messages from

receptors in skin and muscles to the central nervous system.

Motor neurons transmit messages from the central nervous system back to the muscles.

Interneurons are where the sensory neuron connects to the motor neuron.

Synapses The space between nerve cellsis called a

synapse. Messages travel here by electricity and special conductor called neurotransmitters.

This space between two cells is known as the synaptic gap. For the signal to cross the synaptic gap, neurotransmitters are used.

Neurotransmitters are found in small synaptic vesicles clustered at the tip of each axon.

Neurotransmitters

Acetylcholine is an example of a neurotransmitter, as is norepinephrine, although each acts in different responses.

Once in the cleft, neurotransmitters are active for only a short time.

Functions Performed by the Nervous System Receive sensory input from inside and

outside of the body. Make sense of this input Respond to the stimuli

There are 2 types of Nervous Systems that you should be aware of…PNS vs. CNS The Peripheral Nervous System (PNS) is all

nerves with the exception of the Brain and Spinal Cord

The Central Nervous System (CNS) is composed only of the brain and spinal cord.

The Peripheral Nervous System

Two main components of the PNS:• Sensory (afferent) pathways that provide input

from the body into the CNS. • Motor (efferent) pathways that carry signals to

muscles and glands (effectors).

Most sensory input carried in the PNS remains below the level of conscious awareness. Input that does reach the conscious level of our brain contributes to perceptions of our external environment.

All but brain and spinal cord!!!

The Reflex Arc

The reflex arc is an automatic, involuntary reaction to a stimulus.

When the doctor taps your knee with the rubber hammer, she/he is testing your reflex (or knee-jerk). The reaction to the stimulus is involuntary, with the CNS being informed but not consciously controlling the response.

Examples of reflex arcs include balance, the blinking reflex, and the stretch reflex.

The Autonomic Nervous System - Part of the PNS The Autonomic Nervous System is that part

of PNS consisting of motor neurons that control internal organs. AUTOMATIC

The autonomic system controls muscles in the heart, the smooth muscle in internal organs such as the intestine, bladder, and uterus.

That was the PNS – now for The Central Nervous System The Central Nervous System (CNS) is

composed of the brain and spinal cord. The CNS is surrounded by bone-skull and vertebrae.

Fluid and tissue also insulate the brain and spinal cord.

The Brain

The brain is composed of three parts: the cerebrum (conscious activity), the cerebellum, and the medulla oblongata (these latter two are "part of the unconscious brain").

The Medulla

The medulla oblongata is closest to the spinal cord, and is involved with the regulation of heartbeat, breathing, vasoconstriction (blood pressure), and reflex centers for vomiting, coughing, sneezing, swallowing, and hiccuping.

Involuntary reactions!!!!!!!

Cerebellum

The cerebellum is the second largest part of the brain, after the cerebrum.

It functions for muscle coordination and maintains normal muscle tone and posture. The cerebellum coordinates balance.

Cerebrum

The cerebrum, the largest part of the human brain, is divided into left and right hemispheres.

The hemispheres are covered by a thin layer of gray matter known as the cerebral cortex.

Cerebrum (con’t)

The cerebrum is the center for thought, memory and learning.

It interprets messages from the sense organs and initiates all conscious or voluntary movements.

So...The Cerebrum Deals with...

Motor activity and integration of muscle activity

Speech Thought processes

The Spinal Cord

The spinal cord runs along the dorsal (back) side of the body and links the brain to the rest of the body.

Vertebrates have their spinal cords encased in a series of (usually) bony vertebrae that comprise the vertebral column.

The spinal cord is also involved in reflexes that do not immediately involve the brain.

Cerebral Palsy

Disease caused by damage to parts of the brain that control voluntary movements.

The damage occurs during embryonic development.

Meningitis

Inflammation of the membranes that surround the brain and spinal cord.

Caused by viral or bacterial infections Symptoms include headache, muscle

stiffness, fever and chills.

Stroke

The brain is damaged as a result of a cebrebral hemorrhage or blood clot in a blood vessel in the brain.

Polio

Caused by a virus that affects the central nervous system and may result in paralysis.

Can be prevented by immunization.