Every Conscious Action Is Governed by the Nervous System

Chapter 7 Nervous System Every conscious action is governed by the nervous system Functions  Communication between distant parts of the body  Collection and integration of stimuli (both internal and external  Formation and initiation of appropriate response  Responsible for very rapid responses  Crucial role in maintaining homeostasis  Works in a concerted effort with the endocrine system (slower, longer-lasting responses) The nervous divisions  2 divisions: o Central nervous system (CNS): Brain and spinal cord o Peripheral nervous system (PNS): All of the neurons that extend from the CNS How the two work together  Information is passed from sensory receptors to PNS o Special senses (sight, hearing, smell, taste) o General sensory receptors (touch, light, external heat, pain) o Visceral receptors (monitoring internal organ function)  Information moves from PNS to CNS  Information is processed by the CNS and the appropriate response is determined  Motor response is sent from CNS via PNS to appropriate muscles or glands The peripheral nervous system  Divided into 2 systems: o Somatic o Autonomic  The PNS: Somatic division o Serves the skin, skeletal muscles, and tendons o Mainly involved with conscious actions but also responsible for reflex responses o Automatic responses are called reflexes  The PNS: Autonomic division o Regulates the activity of involuntary muscles (cardiac and smooth) and glands to maintain homeostasis o Divided into 2 divisions: . Sympathetic - coordinates the body for the “fight or flight” response by speeding up metabolism, heart rate, and breathing while down- regulating other functions . Parasympathetic - counters the sympathetic system by promoting a relaxed state by slowing metabolism, heart rate, and breathing and returning other functions to normal The nervous system  2 cell types: neurons and neuroglia  Expanding on neurons o 3 types of neurons: o Sensory – take impulses from sensory receptor to CNS o Interneurons – receive information in the CNS and send it to a motor neuron . These essentially connect the sensory and motor neurons o Motor – take impulses from the CNS to an effector (i.e. gland or muscle fiber)  Nerve impulses move from the dendrite through the cell body and then down the axon  From the axon terminus, the signal is transferred to the next neuron  Nerve impulses  Neurons function because without any impulse, they already have a resting potential o This requires creating a charge imbalance across the cell membrane o The charge imbalance is generated by the Na+/K+ pump (active transport requiring ATP) o The ions remain in place because of gated channels o When neurons “fire” in response to signals, there is a rapid reversal of the charge differential across the membrane o Nerve impulses move from the dendrite through the cell body and then down the axon o From the axon terminus, the signal is transferred to the next neuron  Neurotransmitters o Between adjacent neurons are small spaces called synapses o Neurotransmitters are released by one neuron and received by the next neuron  Synaptic integration o Integration is the summation of the inhibitory and excitatory signals received by a postsynaptic neuron o This occurs because a neuron receives many signals The central nervous system o Consists of the brain and the spinal cord o Both are protected by: o Bones – skull and vertebral column o Meninges – 3 protective membranes that wrap around CNS o Cerebral spinal fluid (CSF) – space between meninges is filled with this fluid that cushions and protects the CNS o Both are made up of 2 types of nervous tissue: o Gray matter – contains cell bodies and nonmyelinated fibers o White matter – contains myelinated axons

The CNS: Brain Four major parts: 1. The brain stem o Midbrain – relay station between the cerebrum and the spinal cord or cerebellum; reflex center for sneezing, hiccuping, swallowing, coughing o Pons – a bridge between the cerebellum and the CNS; regulates breathing rate; reflex center for head movements o Medulla oblongata – reflex centers for regulating breathing, heartbeat, and blood pressure 2. Diencephalon Includes the: Hypothalamus – helps maintain homeostasis (responds to or initiates hunger, sleep, thirst, body temperature, and water balance) and controls the pituitary gland Thalamus – 2 masses of gray matter that receive all sensory input except smell; involved in memory and emotions; also visual and auditory startle reflexes Pineal gland – secretes melatonin that controls our daily rhythms

3. Cerebellum o Receives and integrates sensory input from the eyes, ears, joints, and muscles about the current position of the body o Functions o Maintains posture o Coordinates voluntary movement o Allows learning of new motor skills (i.e. playing the piano or hitting a baseball)

4. Cerebrum – the lobes o Cerebrum – largest portion of the brain o Divided into 4 lobes/hemispheres: o Frontal lobe: primary motor area and conscious thought o Temporal lobe: primary auditory, smell, and speech area o Parietal lobe: primary somatosensory and taste area o Occipital lobe – primary visual area o Cerebrum – the cerebral cortex o Cerebral cortex – thin, outer layer of gray matter: o Primary somatosensory area – sensory information from skeletal muscle and skin o Primary motor area – voluntary skeletal muscle o Association areas – integration occurs here o Processing centers – perform higher level analytical functions, includes areas involved in speech

Higher mental functions o Learning – what happens when we recall and use past memories o Memory – ability to hold a thought or to recall past events o Short-term memory – retention of information for only a few minutes o Long-term memory – retention of information for more than a few minutes and includes the following: o Episodic memory – persons and events o Semantic memory – number and words o Skill memory – performing skilled motor activities (i.e. riding a bike) o Language – depends on semantic (words and their meanings) memory Drugs and drug abuse o Drugs have two general effects on the nervous system - affect the limbic system or promote the action of a certain neurotransmitter o Most drug abusers take drugs that affect dopamine and thus artificially affect the reward circuit to the point they ignore basic physical needs in favor of the drug o Nicotine causes the release of dopamine