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

Somatic NS 1.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 2.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

Cross Section of Spinal Cord From:

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)

Autonomic NS (2) 1.Sympathetic NS –“fight or flight” response –↑ heart rate and muscle contractility –Shifts blood supply from viscera to skeletal muscle 2.Parasympathetic NS –Optimizes physiologic function at rest –Promotes digestion and reproductive functions

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

Spinal cord (1) Functions 1.Conduct neural information between brain and periphery 2.Spinal reflexes (no input from brain) cord extends from base of skull to 1 st lumbar vertebra Lumbar cistern= Contains lumbar and sacral spinal nerves and CSF fluid (site of spinal tap and epidural) From:

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

Spinal cord (3) From: Relays somatosensory information entering the spinal cord from receptors in the periphery Contains motor neurons that innervate skeletal muscle 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

Brain (1) Four anatomical regions 1.Brainstem 2.Cerebellum 3.Diencephalon 4.Cerebrum forebrain

From:

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:

Reticular Formation Network of neurons in brainstem Only portion of brain absolutely essential or life (maintains homeostasis) Major functions 1.Breathing and heart rate 2.Regulates states of behavioral arousal (sleep, wakefulness, attention) 3.Regulates stretch reflexes and muscle tone 4.Modulates sensation of pain

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

Diencephalon 1.Thalamus Relay station for neural information going to and from the cerebrum 2.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

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

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