Chapter 46 The Mammalian Nervous System: Structure and Function Biology 102 Tri-County Technical College Pendleton, SC

Vertebrate Nervous System Brain and spinal cord together constitute the central nervous system (CNS) Information brought to and from CNS by means of enormous network of nerves that make up the peripheral nervous system (PNS) PNS connects to CNS via spinal and cranial nerves NERVE is bundle of axons that carries info about many things simultaneously

Vertebrate NS, cont. Important to distinguish between axon of single neuron and a nerve Some axons of nerve may be carrying info to CNS while other axons in same nerve are carrying info from CNS to organs of body

Getting on my nerve…

Types of Nerves Afferent nerves of PNS bring sensory information to the CNS from receptors in peripheral tissues and organs Efferent nerves of PNS carry motor commands from CNS to the muscles and organs Target muscles/organs which respond by doing something are called EFFECTORS

Simple Reflex Reflex is a simple, automatic response Simplest neural circuit involves synapses between only 2 kinds of neurons (sensory and motor) Knee-jerk reflex is one of simplest (2 neurons) Stretch receptor in quadriceps muscle stimulated by stretching of patellar tendon Activates sensory neuron that carries info to spinal cord where synapses with motor neuron If AP generated in motor neuron, it travels back to quadriceps which contracts and causes forward knee jerk

Motor Division of PNS Motor division of peripheral nervous system comprised of somatic and autonomic nervous systems Somatic systems neurons carry signals to skeletal muscles in response to external stimuli; includes reflexes (automatic responses to stimuli) Often considered voluntary because it is subject to conscious control (well, maybe so and maybe not)

Motor Division, cont. Autonomic nervous system controls primarily “involuntary,” automatic, visceral functions of smooth and cardiac muscles and organs of gastrointestinal, excretory, cardiovascular, and endocrine systems Divided into sympathetic and parasympathetic divisions Work in opposition to each other; if one causes an increase, the other causes a decrease and vice versa

Major Components of CNS Brain with white matter in inner region and gray matter in outer region –Arrangement reversed in spinal cord Brain carries out complex integration for homeostasis, perception, movement, intellect, and emotions Spinal cord (located in vertebral column) receives information from skin and muscles and sends out motor commands for movement

Components of CNS, cont. Both covered with meninges (protective layers of connective tissue) Cerebrospinal fluid fills ventricles in brain and central canal of spinal cord This fluid functions in circulation of hormones, nutrients, & WBCs; and in absorption of shock which cushions the brain

What’s the Matter? White matter is term given regions inside CNS that are dominated by myelinated axons –[ ]ed in inner region of brain Gray matter is term given areas in CNS dominated by neuron bodies, glial cells, and unmyelinated axons –[ ]ed in outer region of the brain

Structures/Functions of Brain Medulla oblongata and Pons: control visceral functions including breathing, heart and blood vessel activity, swallowing, vomiting and digestion –Also coordinate large-scale body movements such as walking Cerebellum functions in balance and coordination of movement

S & F of Brain, cont. Telencephalon: One of five regions of brain formed by 6 th week of fetal development –Arises from forebrain and ultimately forms the cerebrum of the adult brain Cerebrum contains the MOST sophisticated integrating centers

S & F of Brain III Diencephalon: another brain region formed by 6 th week Arises from forebrain Gives rise to epithalamus, thalamus, and hypothalamus All of which are prominent integrating centers of diencephalon Epithalamus includes pineal gland (melatonin) and choroid plexuses (CS fluid)

S & F of Brain IV Thalamus sorts info and sends to appropriate higher brain areas; receives input from cerebrum and from parts of brain involved in emotion and arousal Hypothalamus is one of most important regulators of homeostasis –Source of posterior pituitary hormones (ADH and oxytocin) and releasing hormones for the anterior pituitary

S & F of Brain V –Controls body’s thermostat and centers for regulating hunger and thirst –Plays role in sexual response, mating behavior, fight-or-flight response, and pleasure Cerebral Cortex is largest and most complex part of human brain –Part of cerebrum –Highly folded convolutions

S & F of Brain VI Two hemispheres connected by thick band of fibers (white matter) known as corpus callosum Four lobes per hemisphere In response to stimuli, motor complex sends appropriate commands to skeletal muscles Somatosensory cortex receives/integrates signals from touch, pain, pressure, and temperature receptors

OK, enough of this S & F of Brain, already…. Special senses (vision, hearing, smell, and taste) are integrated by cortical regions Corpus callosum allows the two hemispheres of the cerebral cortex to communicate with each other…