Nervous SystemPage 203

Nervous System

•Directs the functions of all human body systems

•100 billion nerve cells•Divided into two sections

▫Central Nervous System▫Peripheral Nervous System

Somatic Autonomic

Neurons

•Contain 3 parts▫Cell body ▫Dendrites▫Axon

Covered by ‘Myelin Sheath’•Two basic properties

▫Excitability – the ability to respond to a stimulus

▫Conductivity – the ability to transmit a signal

Neuroglias

•Cells in the nervous system ▫Support▫Connect▫Protect▫Remove

Debris from the nervous system•Do NOT transmit impulses•Form “blood-brain barrier”

Central Nervous System▫Composed of brain and spinal cord▫Brain has 4 major divisions

Brainstem Cerebellum Cerebrum Diencephalon

Brainstem

•Midbrain▫Visual reflexes

•Pons▫Controls respiratory functions

•Medulla oblongata▫Regulate heart and lung functions▫Swallowing, vomiting, coughing, sneezing

Cerebellum

•Coordinates musculoskeletal movement to maintain posture, balance, and muscle tone

• Cerebral cortex▫Decision making

• Frontal lobe▫Voluntary motor movements▫Emotional expression ▫Moral behavior

• Parietal lobe▫Controls and interprets the senses and tastes

• Temporal lobe▫Controls memory, equilibrium, emotion, and

hearing• Occipital lobe

▫Controls vision and various forms of expression

Cerebrum

Diencephalon

•Contains ▫Thalamus▫Hypothalamus

•Serves as relay center for sensations•Works with the Autonomic nervous

system to control heart rate, blood pressure, temperature, electrolyte balance, digestive functions, behavioral responses, and glandular activities

Central Nervous System

•Cerebrospinal fluid (CSF)▫Watery fluid- flows in and around brain and

spinal cord▫Cradles and cushions the brain

•Spinal cord▫Extends from the base of the brain – L1

Meninges•Three layers of membranes that cover the

brain and spinal cord▫Dura mater

Tough, fibrous membrane that contains channels for blood to enter brain tissue

▫Arachnoid membrane Weblike structure that runs across the space

containing CSF▫Pia mater

Innermost layer, a thin membrane containing many blood vessels that nourish the spinal cord

Peripheral Nervous System

•12 pairs of cranial nerves ▫Carry impulses to and from the brain

•31 pairs of spinal nerves▫Carry messages to and from the spinal cord

and extremities of the body•Somatic Nervous System•Autonomic Nervous System

Somatic Nervous System•Receive and process sensory

input from ▫Skin▫Muscles▫Tendons▫Joints▫Eyes▫Nose▫Ears

•Excite the voluntary contraction of skeletal muscles

Autonomic Nervous System

•Carry impulses from the central nervous system to▫Glands▫Involuntary muscles▫Cardiac muscle

•Sympathetic▫Operates when the body is under stress

•Parasympathetic▫Operates to keep the body in homeostasis