Chapter 6: The Nervous System

Spinal cord

extends from the brain stem down to the beginning of the lumbar region of the spine. It serves as a major pathway for relaying sensory impulses to the brain and motor impulses from the brain.

Cranial nerves

relay impulses to and from the left and right sides of the brain.

Impulse Transmission

- Saltatory conduction in which results in a faster impulse transmission than in nonmeylinated axons

Neurons

- cell body includes a nucleus and mitochondria -dendrites: collect stimuli and transport them to the cell body. While axons transmit impulses away from the cell. - myelin sheath: this overs around the axon within the PNS - neurilemma: The external covering of the Schwann cell, outside the myelin sheath - nodes of Ranvier: The uninsulated gaps, where the axon is exposed between the Schwann cells. - synapse: the intersection including the synaptic cleft.

Two Major Divisions

- central nervous system: this includes the brain and the spinal cord. Directing the activity of the nervous system. - peripheral nervous system: these are the other parts of the nervous system that are not the brain and the spinal cord. The PNS includes the spinal nerves. These spinal nerves transmit messages to and from the brain. - afferent (sensory) nerves: are the nerves that transmit impulses from sensory receptors in the skin, muscles, and joints to the CNS. - efferent (motor) nerves: the nerves that carry impulses from the CNS out to the muscles and glands

Action Potentials

- polaarized: when a neuron is inactive or at rest, where the inside of teh cell membrane is more negatively charged than the outside. - depolarized: when the stimulus exceeds the critical voltage and all the channels open in the cell membrane. - nerve impulse, or action potential, and it executes in an all-or-none fashion. -This begins the process of restoring the membrane to its original, polarized resting state, a process called re-polarization. - The time between the completion of the action potential and repolarization is called the refractory period.

Endoneurium

Each nerve consists of a collection of axons (nerve fibers) and nutrient-supplying blood vessels, all bundled in a series of protective sheaths of connective tissue.

Perineurium

Groups of these sheathed fibers are bundled into fascicles

Transmission at Synapses

Reflexes: simple, rapid, involuntary, programmed responses to stimuli. - somatic reflexes: are those that involve stimulation of skeletal muscles. - automatic reflexes: are those that send involuntary stimuli to the cardiac muscles of the heart annd the smooth muscles of internal organs.

Functional Anatomy Central Nervous System

The Brain: - cerebrum: the left and right cerebral hemispheres. making up the larger portion of the brain. - lobes: the sulci divide the brain into four regions - fissures: uniformly positioned, deep grooves in the brain. - frontal lobes: located behind the forehead in the most anterior portion of the brain. - primary motor cortex: sends neural impulses to the skeletal muscles to initiate and control the development of muscle tension and movement of our body parts. - parietal lobes: located posterior to the frontal lobes. THese include the primary somatic sensory cortex, which interprets sensory impulses received from the skin. - occipital lobes: posterior to the parietal lobes, are responsible fr vision. - temporal lobes: most inferior lobes, involved in speech, hearing, vision, memory, and emotion.

Dorsal Ramus and Ventral Ramus

The spinal nerves are only about one-half inch long, immediately dividing

The Efferent Nerves

Two Functional Subdivisions of the Efferent Nerves: - somatic nervous system: this stimulates the skeletal muscles, causing them to develop tension - autonomic nervous system: controls the cardiac muscles of the heart and the smooth muscles of the internal organs. • Ependymal cells form a protective covering around the spinal cord and central cavities within the brain. • Oligodendrocytes wrap around nerve fibers and produce a fatty insulating material called myelin. The PNS includes two forms of glial cells: • Schwann (shwahn) cells form the fatty myelin sheaths around nerve fi bers in the PNS. • Satellite cells serve as cushioning support cells.

Cerebellum

below the occipital lobe, looks similar to the cerebrum with its outer gray cortex, convolutions, and dual hemispheres

Spinal Nerves

branch out from the left and right sides of the spinal cord. Each pair is named for the vertebral level from which it originates.

Meninges

surround the brain and spinal cord