The Nervous System
Functions of the Nervous System 1. Control center for all body activities 2. Responds and adapts to changes that occur both inside and outside the body (Ex: pain, temperature, pregnancy)
Anatomy of a Neuron Each neuron contains: Cell body : The central cell body is the largest part of a neuron and contains the neuron's nucleus. The cell body produces proteins needed for the construction of other parts of the neuron. Dendrites : fibers that receive messages from other neurons Axons : fibers that send messages to other neurons Myelin Sheath : A fatty, axonenwrapping sheath that serves to speed up neural conduction, formed by concentric layers of Schwann's cell
Myelin Sheath and Neurilemma:* Formation Marieb 11.5abc
Anatomy of a Neuron Neurons do NOT touch; there is a gap between them called a synapse Messages are sent across the synapses by special chemicals called neurotransmitters
Two Major Divisions of the Nervous System
Central Nervous System Central Nervous System: the complex of nerve tissues that controls the activities of the body. In vertebrates it comprises the brain and spinal cord. Neurons : microscopic nerve cells that make up the brain, spinal cord, and nerves 30,000 neurons can fit on a pinhead
Central Nervous System Brain : a mass of 100 billion neurons located inside the skull Learning occurs as more and stronger connections are made between neurons
Anatomy of the Brain Cerebrum : largest part of human brain Responsible for: Thought Language Senses Memory Voluntary movement
Anatomy of the Brain Cerebellum : at base of brain Responsible for: Muscle coordination Balance Posture
Anatomy of the Brain Brain Stem : connects brain to spinal cord Responsible for: Breathing Swallowing Heartbeat Blood pressure
Central Nervous System Continued Spinal Cord : Column of nerves from brain to tailbone protected by vertebrae of spine Responsible for: Conducting impulses between the brain and the rest of the body *Impulses may travel as fast at 268 miles/hr
Peripheral Nervous System Nerves : visible bundles of axons and dendrites that extend from the brain and spinal cord to all other parts of the body
Responsibilities: Sensory nerves carry messages from body to brain (pain, pressure, temperature) Motor nerves carry messages from brain to body to respond
Peripheral Nervous System: Somatic vs Autonomic Somatic Associated with voluntary control of body movements Skeletal muscles used to do this. Three parts Spinal Nerves Cranial Nerves Association Nerves Autonomic Controls involuntary body functions. Respiration Heart Rate Divided into 2 groups Sympathetic Parasympathetic
Divisions of the autonomic nervous system Parasympathetic division Sympathetic division Serve most of the same organs but cause opposing or antagonistic effects Parasysmpathetic: routine maintenance rest &digest Sympathetic: mobilization & increased metabolism fight, flight or fright or fight, flight or freeze 16
Parasympathetic Rest and Digest cardiac output: decreases cardiac muscle: Heart rate decreases smooth muscles of bronchioles: contracts pupil of eye: contracts salivary glands: secretions stimulates watery secretions GI tract: increases smooth muscles of GI tract: contracts sphincters of GI tract: relaxes glands of GI tract: secretes
Sympathetic Fight, Flight, or Freeze cardiac output: increases cardiac muscle: heart rate increases vascular smooth muscle : Contracts smooth muscles of bronchioles:relaxes pupil of eye: relaxes salivary glands: stimulates viscous smooth muscles of Gastro Intestinal tract: relaxes sphincters of GI tract: contracts glands of GI tract: inhibits
Types of Neurotransmitters Marieb 14.2
Action Potentials Brief, rapid, large (100mV) changes in membrane potential: potential actually reverses Involves only a small portion of the total excitable cell membrane All or nothing Conduction without decrement