The Central and Peripheral Nervous SystemBiology II

Divisions of the Nervous System

• Central Nervous System•Brain•Spinal Cord

• Peripheral Nervous System•All nerves that exist outside the CNS, including:•Sensory neurons that carry signals towards the brain.•Motor neurons (voluntary and involuntary) that carry signals from the brain to a muscle or organ.

Central(brain and

spinal cord)

Nervoussystem

Autonomic (controlsself-regulated action of

internal organs and glands)

Skeletal (controlsvoluntary movements of

skeletal muscles)

Sympathetic (arousing)

Parasympathetic (calming)

PeripheralCentral

(brain andspinal cord)

Nervoussystem

Autonomic (controlsself-regulated action of

internal organs and glands)

Skeletal (controlsvoluntary movements of

skeletal muscles)

Sympathetic (arousing)

Parasympathetic (calming)

Peripheral

Neurons

• Neurons are cells specialized in transmitting and receiving messages. •Dendrites conduct impulses towards the cell body.•The cell body contains the nucleus and organelles.•Axons conduct impulses away from the cell body.

How Do Neurons Send Signals?

• All nerve signals are electrical impulses sent down the entire neuron.• A stimulus is required before a nerve

impulse begins – either from another neuron or from one of the senses.

Synapse Signal Transmission

• A synapse is a gap between the axon and dendrite of two neurons.•A neurotransmitteris released from the axon of the previous neuron.•The dendrite of the next neuron has receptors that are stimulated by this signal.

Neuron Polarization

• A resting neuron has more positive ions (K+) inside the cell than outside (Na+). •This results in an overall negative charge across the cell membrane.

Neuron Polarization

Depolarization occurs when a stimulus (such as a neurotransmitter) causes a protein channel to open. Na+ ions flood inside the cell membrane.•This results in an overall positive charge across the cell membrane.

Neuron Polarization

• Once the nerve impulse begins, it travels across the entire length of the axon. • Repolarization; the return to the

original negative charge, occurs as potassium ions flood out of the cell.•The overall result is a nerve cell with a negative charge, low concentration of K+ ions, and a high concentration of Na+ ions.

Neuron Polarization

• The original concentration of ions in the axon is restored by the sodium-potassium ATP pump. •This is an active transport protein channel.•Energy is not needed to transmit a nerve signal, but is needed to restore the neuron so it can transmit again.

Reflexes

• A reflex is a rapid, involuntary response to a stimulus. •These actions occur more quickly than most responses because they occur over a reflex arc, a pathway that bypasses the brain.

The Reflex Arc

• A reflex arc begins with a stimulus at a sensory neuron, such as in the skin.• The sensory neuron is depolarized,

and the signal is sent through its axon.

The Reflex Arc

• The signal is passed across a synapse in the spinal cord to a short interneuron, then to a motor neuron.

The Reflex Arc

• The signal from the motor neuron reaches the end of its axon, and releases a neurotransmitter. • The muscle contracts in response to

the neurotransmitter, and the reflex is complete.

Reflexes

• Reflexes may occur with skeletal muscles•Moving your hand away from a source of pain.

• …or in smooth muscles.•Peristalsis in the small intestines in response to an influx of digested food.

External Brain Anatomy

The Central Nervous System - Brain

• Cerebral Hemisphere (cerebrum)•Left and right superior regions of the brain.•Makes up the majority of brain mass.

• The cerebrum is divided into different regions based on function.

Left vs. Right.

Left vs. Right

Cerebrum

Brain activity when hearing, seeing, and speaking words

Frontal Lobe

• The frontal lobe controls movement, language, and other higher-thinking functions.

Temporal Lobe

• The temporal lobe contains the auditory, taste, and olfactory areas.

Parietal Lobe

• The parietal lobe integrates sensory information.

Occipital Lobe

• The occipital lobe contains the vision center.

Layers of the Cerebrum• The cerebrum has two layers:•Outer grey matter that contains neuron cell bodies.• Inner white matter that contains glial cells and neuron axons.• Glial cells provide support to neurons.

Inner Brain Anatomy

The Diencephalon

• Region of the brain directly on top of the brain stem, within the cerebrum.•Thalamus – Transfers impulses received from sensory neurons to the correct region of the cerebrum.•Hypothalamus – Controls many aspects of internal homeostasis, including body temperature, water balance, and overall metabolism.• Connected is the pituitary gland, which releases

several hormones that control metabolism, puberty, and a wide variety of other glands.

The Brain Stem

• This attaches the brain directly to the spinal cord.•The pons contains the neurons responsible for controlling breathing.•The medulla oblongata is the lowest part of the brain stem, merging into the spinal cord.• Controls heart rate, blood pressure,

swallowing, vomiting.

Cerebellum

• Coordinates body movements.

Protection of the CNS• Bone• Meninges•Connective tissue membranes that cover the central nervous system.•Dura mater is the outermost thickest layer.

Protection of the CNS

• Meninges•Arachnoid mater is a web-like network of blood vessels.•Pia mater is the innermost layer.

Protection of the CNS

• Cerebrospinal fluid, similar to plasma, circulates through a series of cavities called ventricles throughout the brain.•Provides a watery cushion that protects nervous tissue from trauma.

• A blood-brain barrier, made of capillaries, only allows water, glucose, and amino acids into the brain area.•Wastes, proteins, and cells are kept out.

Spinal Cord

• Continuation of the brain stem down the back towards the pelvis.• All protective barriers from the brain,

including the bone (spinal column) and meninges are present.• 31 pairs of nerves leave the spinal

cord and connect to various organs and muscles.

CNS Disorders

• Encephalitis is an inflammation of the brain itself, caused by a foreign substance or a virus.•Headache, drowsiness, nausea, fever.

• Meningitis is an inflammation of the meninges (membranes) of the brain and spinal cord.•Fever, stiff neck

CNS Disorders

• Alzheimer’s•A degenerative disease that causes a gradual loss of neuron cell bodies and synapses in the cerebral cortex.•Tends to affect new memories first.•Cause unknown.

CNS Disorders

• Creutzfeldt-Jakob Disease•Human equivalent of Mad Cow disease.•Caused by prions (infectious proteins) that convert normal neuron proteins into more prions.•Gradually causes small holes to appear in brain tissue as more and more nervous tissue becomes disabled.

CNS Disorders

• All tumors are dangerous, but brain tumors especially so, due to the difficulty of removing and treating them.•Symptoms vary depending on the exact region affected by the tumor.

CNS Disorders

• Multiple sclerosis is an autoimmune disorder where the myelin sheaths surrounding neuron axons are damaged.•These sheaths serve to insulate the axons, greatly increasing nerve signal speed.•Symptoms include degeneration senses (vision, touch, etc) muscle weakness, and depression.

CNS Disorders

• A stroke occurs when a blood clot or ruptured blood vessel interrupts blood flow to a specific part of the brain.•Brain cells die from lack of oxygen, causing permanent damage in that region.•Brain equivalent of a heart attack.

Peripheral Nervous System

• The peripheral nervous system includes all neurons outside of the brain and spinal cord.•Sensory neurons•Motor neurons•Cranial nerves•Spinal nerves

Cranial Nerves

• The cranial nerves are 12 pairs of nerves, mostly from the head and neck, that attach directly to the brain.•Bypass the spinal cord.

Cranial Nerves

I. Olfactory• Smell (sensory)

II. Optic • Vision (sensory)

III.Oculomotor• Eye muscles (motor)

IV.Trochlear• Eye muscles (motor)

V. Trigeminal• Facial (sensory) , chewing muscles (motor)

VI.Abducens• Eye muscles (motor)

Cranial Nerves

VII.Facial• Taste (sensory), facial muscles (motor)

VIII.Vestibulocochlear• Balance and hearing (sensory)

IX.Glossopharyngeal• Taste (sensory), swallowing (motor)

X. Vagus• Sensory and motor neurons that affect

sweating, peristalsis, heart rate, opening the larynx for speech and breathing.

• Has branches in the ear canal – cotton swab cough.

Cranial Nerves

XI.Accessory Nerve• Neck and upper back muscles

(motor)

XII.Hypoglossal• Tongue (motor)

Spinal Nerves

• A total of 31 pairs of nerves exit the spine towards different organs and muscles.• These are part of

the autonomic nervous system.

Autonomic Nervous System

• The autonomic nervous system includes all neurons that control involuntary actions around the body.• Parasympathetic nerves tend to

originate from the cranial and sacral areas of the CNS.•Controls “rest and digest” functions within the body.•Salivation, tears, urination, digestion, defecation, and sexual arousal.

Parasympathetic Nerves

Autonomic Nervous System

• Sympathetic nerves tend to originate from the thoracic and lumbar regions of the spine.•Controls “fight or flight” responses within the body.•Dilates pupils, increases heart rate, activates sweat glands, inhibits peristalsis, and promotes ejaculation.

Sympathetic Nerves

1. Olfactory nerve

• 1. Olfactory= used for the sense of smell• Elongated and enlarged in most animals other than humans.

2. Optic Nerve

• Responsible for vision.• Optic Chiasm= where the two optic nerves cross over. (Makes an X)

3. Oculomotor

• 3. Oculomotor= moves the eyes. • Helps control the muscles that move the eyes. • Six muscles on each eye.• Three Nerves for each eye to give you binocular vision

(lazy eye)

5. Trigeminal nerve

• 5. Trigeminal Nerve= largest we will see• Somatosensory Information (Touch and Pain)• From face and head• Also controls chewing muscles and tooth pain

10. Vagus Nerve

• Vagus Nerve= thin thread down side of trachea and common carotids.• Sensory and motor autonomic functions of the viscera (glands, digestion, heart rate, breathing)