Anatomy and Physiology - The Nervous System

What are the two great control systems of the body?

Nervous and Endocrine systems

3 main overlapping functions of the nervous system?

Sensory input, integration, motor output

Central Nervous System (CNS)

Comprised of brain and spinal cord

Peripheral Nervous System (PNS)

Comprised of nerves outside the brain and spinal cord

Sensory (afferent) division

Carries information to the CNS; subdivision of PNS

Motor (efferent) division

Carries information from the CNS to muscles and glands; subdivision of PNS

Somatic nervous system

Voluntary and used to control skeletal muscles

1 motor neuron

Autonomic nervous system

Involuntary and controls activity of smooth and cardiac muscles and glands

2 motor neurons: preganglionic and postganglionic

Sympathetic nervous system

Stimulus for flight-or-fight response (stress); su

Parasympathetic nervous system

Maintains homeostasis

What is nervous tissue comprised of?

Neurons and neuroglia (supporting cells)

3 functions of neuroglia cells?

Support, insulate, and protect neurons

Describe the anatomy of neurons

Made of cell body and processes

Nissl Substance

Specialized rough endoplasmic reticulum

Neurofibrils

Cytoskeleton that maintains cell shape

Dendrites

Conduct impulses towards the cell body

Axons

Conduct impulses away from the cell body

Axon hillock

Where axons arise from

Synaptic Cleft

Gap between adjacent nerurons

Synapse

Junction between neurons

Microglia

Phagocytes

Disposes of debris in the CNS

Astrocytes

Anchor neurons to capillaries

Helps protect neurons from harmful substances in the blood

Controls the chemical environment of the brain by picking up excess ions and recapturing released ions

Ependymal Cells

Line cavities of brain and spinal cord

Their cilia circulates cerebrospinal fluid (CSF)

Oligodendrocytes

Produce myelin sheath around nerve fibers in CNS

This increases transmission of impulses

Satellite cells

Protect neuron cell bodies in PNS

Schwann cells

Form myelin sheath in PNS

Nodes of Ranvier

Gaps in myelin sheath along the axon

Allows impulse to jump faster from node to node

Gray matter

Unmyelinated regions of CNS

Cell bodies and unmyelinated fibers

White matter

Myelinated regions of CNS

Myelinated fibers (tracts)

Nuclei

Clusters of cell bodies in the CNS

Ganglia

Clusters of cell bodies in the PNS

Tract

Bundles of nerve fibers in the CNS

Nerve

Bundles of nerve fibers in the PNS

Sensory (afferent) neurons

Cell body in the PNS

Carry impulses from sensory receptors

Motor (efferent) neurons

Cell body in CNS

Carry impulses from CNS

Interneurons (association neurons)

Found in neural pathways in the CNS

Connect sensory and motor neurons

Multipolar neurons

Many extensions (dendrites) from the cell body

Most are motor neurons

Bipolar neurons

Have one axon and one dendrite

Found in special neurons in eyes or ears

Unipolar neurons

Have a short single process leaving the cell body

Most are sensory neurons

Irritability

Ability to respond to stimuli

Conductivity

Ability to transmit and impulse

Reflex

Rapid, predictable, involuntary response to stimuli

Reflex arc

Direct route from sensory neuron, to interneuron, to motor neuron

Autonomic reflex

Smooth muscle regulation

Heart and blood pressure regulation

Regulation of glands

Digestive system regulation

Somatic reflex

Activation of skeletal muscles

4 regions of the brain?

Cerebral hemispheres (cerebrum)

Diencephalon

Brain stem

Cerebellum

Cerebral hemispheres

Paired (left and right) superior parts of brain

Responsible for thought, foresight, planning, sensory awareness, conscious movement

Frontal, occipital, temporal, parietal lobes

Gyri

Ridges in the brain's surface

Sulci

Grooves in the brain's surface

Occipital lobe

Responsible for vision

Frontal lobe

Responsible for muscle movement

Temporal lobe

Responsible for speech, hearing, and smell

Parietal lobe`

Contains the somatic sensory area

Corpus Callosum

Very large fiber tract that connects the two hemispheres

Basal Nuclei

Islands of gray matter that regulate muscle activity

Diencephalon

Enclosed by central hemispheres

Consists of thalamus, hypothalamus, and epithalamus

Thalamus

Surrounds the third ventricle

Relay station for sensory impulses

Hypothalamus

Maintains homeostasis: regulates body temperature, controls water balance, regulates metabolism

Part of the Limbic system; dopamine (thirst, appetite, sex, pain, pleasure centers)

Regulates pituitary gland

Epithalamus

Forms roof of third ventricle

Houses the pineal body (secretes melatonin)

Includes the choroid plexus (forms CSF)

Amygdala

Fear response (fight-or-flight)

Hippocampus

Long-term memory storage

Brain stem

Attaches to spinal cord

Consists of midbrain, pons, medulla oblongata, and the reticular formation

Midbrain

Mostly composed of tracts of nerve fibers

2 bulging fiber tracts: cerebral peduncles

4 rounded protrusions: corpora quadrigemina (reflex centers for vision and hearing)

Pons

Bulging center part of brain stem

Mostly composed of fiber tracts

Includes nuclei involved with control of breathing

Medulla Oblongata

Lowest part of brain stem

Merges into spinal cord

Contains control centers for: heart rate, blood pressure, breathing, swallowing, vomiting

Reticular Formation

Mass of gray mater extending along the brain stem

Neurons here involved with motor control of visceral organs

Reticular Activating System (RAS) plays a role in sleep/wake cycles

Damage here can result in a permanent coma

Meninges

3 layers of covering around CNS

Made of connective tissue

Dura Mater, Arachnoid layer, Pia Mater

Dura Mater

2 layers of protection around brain: periosteum attached to skull and meningeal outside of the periosteal layer

1 layer of protection around the spinal cord: meningeal

Arachnoid layer

Middle layer of protection that is web-like

Pia Mater

Internal layer that clings to the surface of CNS

Cerebrospinal Fluid (CSF)

Forms a watery cushion to protect nervous tissue of CNS from blows and other trauma

Similar composition to blood plasma

Formed from blood by choroid plexus

Circulated in arachnoid space, ventricles, and central canal of spinal cord

Blood Brain Barrier

Least permeable capillaries in the body

Permeable to: water, glucose, essential amino acids, fats and fat soluble molecules, respiratory gases, alcohol, nicotine, anesthesia

Not permeable to: metabolic wastes, most drugs, non-essential amino acids

Spinal cord anatomy?

Extends from medulla oblongata to the L2 lumbar vertebrae

Below L2: cauda equina (collection of spinal nerves)

Functions: reflexes, motor signals from here go to effectors, sensory signals pass through en route to the brain

Endoneurium

Surrounds each fiber

Perimeurium

Surrounds each fascicle (group of fibers)

Epineurium

Surrounds each nerve (group of fascicles)

Mixed nerves

Have both sensory and motor fibers

Afferent (sensory) nerves

Carry impulses toward CNS

Efferent (motor) nerves

Carry impulses from CNS

Cranial nerves

12 pairs of nerves that serve head and neck (except vagus)

Most are mixed nerves

Olfactory nerve

Sensory nerve for smell

Optic nerve

Sensory nerve for vision

Trigeminal nerve

Sensory nerve for the face

Motor fibers for chewing muscles

Facial nerve

Sensory nerve for taste

Motor fibers for face

Vestibulocochlear nerve

Sensory nerve for balance and hearing

Glossopharyngeal nerve

Sensory nerve for taste

Motor fibers to the pharynx (swallowing/saliva production)

Vagus nerve

Motor nerve for digestion and regulation of the heart

Spinal nerves

31 pairs of mixed nerves

Formed by combination of ventral and dorsal roots of spinal cord

Named for the region in which they arise

Dorsal rami

Network of nerves that serve the skin and muscles of the posterior trunk

Ventral rami

Forms a complex of networks (plexus) for the anterior and lateral sides of the body and intercostal muscles (between ribs)