CHAPTER 28 Nervous System

28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands The nervous system has three interconnected functions –Sensory input: receptors-structures specialized to detect certain stimuli –Integration: through the spinal cord & brain –Motor output: effectors-respond to a stimulus such as muscles or glands

28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands II

Nervous System Central nervous system –brain & spinal chord Peripheral nervous system –nerves from senses –nerves to muscles cerebrum cerebellum spinal cord cervical nerves thoracic nerves lumbar nerves femoral nerve sciatic nerve tibial nerve

Three types of neurons correspond to the nervous system’s three main functions –Sensory neurons convey signals from sensory receptors into the CNS –Interneurons integrate data and relay signals –Motor neurons convey signals to effectors

Types of neurons sensory neuron (from senses) interneuron (brain & spinal chord) motor neuron (to muscle)

28.2 Neurons are the functional units of nervous systems Neurons are cells specialized to transmit nervous impulses They consist of –a cell body ~contains the nucleus –dendrites (highly branched fibers) stimulus toward cell body –an axon (long fiber) carries impulses away from cell body

signal direction myelin coating Myelin coating  Axon coated with insulation made of myelin cells  speeds signal  signal hops from node to node (Nodes of Ranvier)  330 mph vs. 11 mph Multiple Sclerosis  immune system (T cells) attacks myelin coating  loss of signal Multiple Sclerosis  immune system (T cells) attacks myelin coating  loss of signal

Supporting cells protect, insulate, and reinforce neurons The myelin sheath is the insulating material in vertebrates –It is composed of a chain of Schwann cells linked by nodes of Ranvier –It speeds up signal transmission –Multiple sclerosis (MS) involves the destruction of myelin sheaths by the immune system

NERVE SIGNALS AND THEIR TRANSMISSION 28.3 A neuron maintains a membrane potential across its membrane The resting potential of a neuron’s plasma membrane is caused by the cell membrane’s ability to maintain –Polarity – outside axon membrane + – Inside axon membrane - Resting potential is generated and maintained with help from sodium- potassium pumps –These pump K + into the cell and Na + out of the cell

28.4 A nerve signal begins as a change in the membrane potential A stimulus alters the permeability of a portion of the plasma membrane –Ions pass through the plasma membrane, changing the membrane’s voltage –It causes a nerve signal to be generated An action potential is a nerve signal –It is an electrical change in the plasma membrane voltage from the resting potential to a maximum level and back to the resting potential

28.5 The action potential propagates itself along the neuron An action potential is an all-or-none event

28.6 Neurons communicate at synapses –It is a junction or relay point between two neurons or between a neuron and an effector cell Synapses are either electrical or chemical –Action potentials pass between cells at electrical synapses –At chemical synapses, neurotransmitters cross the synaptic cleft to bind to receptors on the surface of the receiving cell

28.9 Connection: Many drugs act at chemical synapses Drugs act at synapses and may increase or decrease the normal effect of neurotransmitters –Caffeine –Nicotine –Alcohol –Prescription and illegal drugs

28.12 The peripheral nervous system of vertebrates is a functional hierarchy Peripheral nervous system Sensory division Motor division Autonomic nervous system (involuntary Somatic nervous system (voluntary Sympathetic division Parasympathetic division Sensing external environment Sensing internal environment

28.13 Opposing actions of sympathetic and parasympathetic neurons regulate the internal environment –The parasympathetic division primes the body for activities that gain and conserve energy –The sympathetic division prepares the body for intense, energy-consuming activities

28.15 The structure of a living supercomputer: The human brain

28.15 The structure of a living supercomputer: The human brain II

Primitive brain The “lower brain” –medulla oblongata –pons –cerebellum Functions –basic body functions breathing, heart, digestion, swallowing, vomiting (medulla) –homeostasis –coordination of movement (cerebellum)

Higher brain Cerebrum –2 hemispheres –left = right side of body –right = left side of body Corpus callosum –connection between 2 hemispheres

Division of Brain Function Left hemisphere –“logic side” –language, math, logic operations, vision & hearing details –fine motor control Right hemisphere –“creative side” –pattern recognition, spatial relationships, non-verbal ideas, emotions, multi-tasking

Cerebrum specialization frontal temporal Regions specialized for different functions Lobes –frontal speech, control of emotions –temporal smell, hearing –occipital vision –parietal speech, taste reading occipital parietal

Limbic system Controls basic emotions (fear, anger), involved in emotional bonding, establishes emotional memory

Simplest Nerve Circuit  Reflex, or automatic response  rapid response  automated  signal only goes to spinal cord  no higher level processing  advantage  essential actions  don’t need to think or make decisions about  blinking  balance  pupil dilation  startle

cerebrum cerebellum spinal cord cervical nerves thoracic nerves lumbar nerves femoral nerve sciatic nerve tibial nerve Any Questions??