chapter 46 the mammalian nervous system: structure and function
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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) - PowerPoint PPT PresentationTRANSCRIPT
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
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 6th 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
6th 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