Divisions of the Divisions of the Nervous SystemNervous System

Chapter 7

Divisions of the Nervous Divisions of the Nervous SystemSystem

• 2 major divisions:

Nervous System

Central Nervous System

Peripheral Nervous System

BrainSpinal Cord

Nerve cells

A. The Central Nervous System (CNS)• Control center of the

body• Relays messages,

processes & analyzes information

• Made of two parts:– BrainBrain– Spinal cordSpinal cord

• 1. The Brain1. The Brain– Impulses flow to and from the

brain– 100 billion neurons, mainly

interneurons

•2. Spinal Cord– Main

communication link between brain and the rest of the body

– Processes information such as reflexes

1. Protection of the CNS• Brain and spinal cord are protected by:• a) Bone – skull and vertebrae• b) Meninges – layers of connective

tissue that surround the organs• c) Cerebrospinal fluid – fluid found in

between meninges and organ– Acts as a shock absorber– Continually circulates around the brain

• DISEASE: Meningitis– Inflammation of the meninges– Can be caused by an viral ,

bacterial or microorganism infection

– Causes headaches, neck stiffness, confusion, sensitivity to light and sound

– Can be life threatening • DISEASE: Hydrocephalus

(“water on the brain”)– Accumulation of CSF in the

brain– Exerts pressure on the brain

causing brain damage

2. Regions of the Brain• Regions of the Brain

–Cerebral hemispheres (Left & Right)

–Diencephalon–Brain stem–Cerebellum

a. Cerebral Hemispheres a. Cerebral Hemispheres (Cerebrum)(Cerebrum)

• Left and right hemispheres– Left brain – logic,

language, math– Right brain – creativity

• Connected by the corpus callosum (communication link between right and left)

• The surface is made of ridges (gyri) and grooves (sulci)

Fissures Fissures (deep grooves) (deep grooves) divide the cerebrum divide the cerebrum into four lobesinto four lobes

1.1. Occipital LobeOccipital Lobe: visual integration

2.2. ParietalParietal: spatial knowledge, math

3.3. TemporalTemporal: memories, auditory, language

4.4. FrontalFrontal: emotion, future planning, judgment, muscle movements, language

• Limbic System – involved in emotion, motivation, arousal, memory, and learning– Amygdala – fear– Hippocampus –

memory formation

b. Diencephalon• Relay and control center• Sits on top of brain stem• Two main parts:

– 1) Thalamus – relay between sensory areas and cerebrum– 2) Hypothalumus – regulates involuntary responses & hormone secretions of

the pituitary gland

c. Brain Stem• Attaches brain to spinal

cord• Parts of the brain stem

– Midbrain – vision, hearing, motor control

– Pons – breathing, sleep– Medulla oblongata -

involuntary activities (breathing, heart rate, blood pressure)

d. Cerebellum• “Little brain”

inferior to and posterior to cerebral cortex

• Coordination, posture, motor learning

3. Spinal Cord• Cylinder of nervous

tissue that begins at base of brain

• Protected by the vertebral column and meninges

• Spinal nerves extend from the cord through each vertebrae

• Main communication link between brain and the body

4. Traumatic Brain Injuries & Diseases• Concussion

– Slight or mild brain injury– Bleeding & tearing of nerve fibers

happened– Recovery likely with some memory loss

• Contusion– A more severe TBI– Nervous tissue destruction occurs– Nervous tissue does not regenerate

• Cerebral edema– Swelling from the inflammatory

response– May compress and kill brain tissue

• Cerebrovascular Accident (CVA)Cerebrovascular Accident (CVA)– Commonly called a stroke– The result of a blocked or ruptured

blood vessel supplying a region of the brain

– Brain tissue supplied with oxygen from that blood source dies

– Loss of some functions or death may result

Alzheimer’s Disease• Progressive degenerative brain disease• Mostly seen in the elderly, but may

begin in middle age• Structural changes in the brain include

abnormal protein deposits and twisted fibers within neurons

• Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death

Peripheral Nervous System Peripheral Nervous System (PNS)(PNS)

Sensory Division Motor Division

Somatic NS Autonomic NS

Sympathetic Parasympathetic

B. Peripheral Nervous System B. Peripheral Nervous System (PNS)(PNS)

• Peripheral Nervous System Peripheral Nervous System is made up of all the nerves and ganglia (nerve cell bodies) that carry messages between the body and the CNS

• Receives info from the environment

• Transmits commands from CNS to organs and glands

• Contains mostly motor and Contains mostly motor and sensory neuronssensory neurons

Divisions of the PNSDivisions of the PNS•Sensory

division –transmits impulses from sense organs to the central nervous system

•Motor division –transmits impulses from the central nervous system to the muscles or glands

–Divided into 2 divisions•Somatic•Autonomic

Motor DivisionMotor Division•Somatic N.S.• Regulates activities

that are under conscious control

• Example: movement of muscles (wiggle toe)

• Involved in reflexes (quick, automatic response to stimulus)

•Autonomic N.S.• Regulates activities

that are automatic or involuntary

• Example: heart rate• Consists of only

motor nerves• Divided into two

divisions– Sympathetic division– Parasympathetic

division

Autonomic N.S. DivisionAutonomic N.S. Division•Sympathetic• “Fight-or-Flight”• Takes over to

increase activities• Remember as the

“E” division = exercise, excitement, emergency, and embarrassment

•Parasympathetic

• “Rest and Digest• Conserves energy• Maintains daily

necessary body functions

• Remember as the “D” division = digestion, defecation, and diuresis (urination)

Peripheral Nervous Peripheral Nervous System & ReflexesSystem & Reflexes

•The peripheral nervous system is also involved in reflexes.

•A reflex is a quick and unconscious response to a stimulus

•The brain is not involved with reflexes.

• The impulse travels up sensory neurons, to the spinal cord (interneuron), then immediately travels down motor neurons for a response.

• The pathway the impulse travels is called the reflex arc

Reflex ArcReflex Arc

• Receptor (sense organ) sensory neuron spinal cord motor neuron effector (muscle)

Internal CommunicationInternal Communication•Internal communication is critical to maintain homeostasis.

•Sensory neurons are constantly sending information to the brain about the internal environment.

•The brain responds by sending signals through the motor neurons to maintain homeostasis.

The Nervous SystemThe Nervous System

PNSPNSCNSCNS

Somatic NSSomatic NSVoluntary Movement

Autonomic NSAutonomic NSInvoluntary Movement

Sympathetic Sympathetic NSNS

fight or flight

ParasympatheParasympatheticticNSNS

rest & digest

BrainBrain Spinal Spinal CordCord