Peripheral NS

1. Peripheral NS • Links the brain to sensor receptors, skeletal muscles, and effector organs in the periphery • Consists of two divisions • somatic nervous system • autonomic nervous system • Terminology • Afferent neurons = toward CNS • Efferent neurons = away from CNS

2. Somatic NS • Sensory neurons that innervate sense organs, skin, muscles, joints, and internal organs • Afferent neurons • Cell body in dorsal root ganglia just outside spinal cord • Axon split into two parts, one that extends toward structure associated with a sensory receptor and another that enters through the dorsal root to the CNS • Motor neurons that innervate skeletal muscle • Efferent neurons = carry signal from CNS to peripheral structures • Cell body in spinal cord and extends out through ventral root of spinal cord

3. Cross Section of Spinal Cord From: http://thalamus.wustl.edu/course/spinal.html

4. Autonomic NS (1) • Often called “involuntary” nervous system • Regulates contraction of smooth muscle of blood vessels and viscera, cardiac muscle, and function of exocrine and (to some extent) endocrine glands • Efferent neurons • Involves chain of two neurons, one preganglionic (cell body in brainstem or spinal cord) and one postganglionic (cell body outside CNS)

5. Autonomic NS (2) • Sympathetic NS • “fight or flight” response • ↑ heart rate and muscle contractility • Shifts blood supply from viscera to skeletal muscle • Parasympathetic NS • Optimizes physiologic function at rest • Promotes digestion and reproductive functions

6. Central NS • Conducts neural signals to and from the peripheral NS • Consists of two components • Spinal cord • Brain

7. Spinal cord (1) Functions • Conduct neural information between brain and periphery • Spinal reflexes (no input from brain) cord extends from base of skull to 1st lumbar vertebra Lumbar cistern= Contains lumbar and sacral spinal nerves and CSF fluid (site of spinal tap and epidural) From: http://faculty.washington.edu/chudler/spinal.html

8. Spinal cord (2) Spinal cord and nerves extend through intervertebral foramen Soft connective tissue that functions as a shock absorber for the spinal column

9. Spinal cord (3) Relays somatosensory information entering the spinal cord from receptors in the periphery Gray matter (inner core) = interneurons, cell bodies and dendrites of efferent neurons, and glial cells White matter (outer layer) = axons covered by white myelin sheath Contains motor neurons that innervate skeletal muscle From: http://thalamus.wustl.edu/course/spinal.html

10. Brain (1) • Four anatomical regions • Brainstem • Cerebellum • Diencephalon • Cerebrum forebrain

11. From: http://www.neurosurgerytoday.org/images/brainmetastasis2.jpg

12. 1. Brainstem • Medulla = transition from spinal cord to brainstem • Pons = functional and anatomic bridge between cerebral cortex and cerebellum • Midbrain = links brainstem to diencephalon, contains nuclei involved in visual and auditory processes From: http://www.sparknotes.com/psychology/neuro/brainanatomy/section7.rhtml

13. Reticular Formation • Network of neurons in brainstem • Only portion of brain absolutely essential or life (maintains homeostasis) • Major functions • Breathing and heart rate • Regulates states of behavioral arousal (sleep, wakefulness, attention) • Regulates stretch reflexes and muscle tone • Modulates sensation of pain

14. 2. Cerebellum • Essential to accurate and precise carrying out of voluntary movement • When damaged, gait, balance and deliberate movements are impaired

15. Diencephalon • Thalamus • Relay station for neural information going to and from the cerebrum • Hypothalamus • Most important structure to maintain homeostasis • Receives info about internal environment directly from sensors in the periphery, integrates this info, then initiates appropriate behavioral, endocrine, and autonomic responses • Regulates eating and drinking behavior, energy balance, and the autonomic, endocrine and behavioral regulation of body temperature • Influences reproductive behavior • Site where brain interacts with endocrine system, through anterior and posterior pituitary glands

16. Cerebrum (1) • Largest and most complex brain structure • Divided into left and right hemispheres, each containing a cerebral cortex and subcortical nuclei • Cerebral cortex has 4 lobes (frontal, parietal, occipital, and temporal) • Subcortical nuclei are gray matter that underlie the myelinated nerve tracts that that relay information to and from regions of the cortex • Involved in posture, initiation of movement, and other aspects of motor control and behavior • Corpus callosum is a band of nerve fibers that forms and anatomic and functional bridge between the two cerebral hemispheres

17. Cerebrum (2) • Important integrating center • Site where sensory information is perceived, voluntary movement is initiated, and thoughts and memories are stored • Conscious mind communicates with the body through the limbic system • Interconnected group of structures that includes portions of the frontal lobe, temporal lobe, thalamus and hypothalamus, and the anatomic connections that link them Note: This ends page 8 of Neuro readings 2 & 3