 Sensors › Monitor external and internal environment  Processing › Receives information, integrates it, and decided what to do  Effectors › Carries messages to effectors and tells them what to do

 Neurons › Main cell of nervous tissue › Relay and process messages  Neuroglial › Provide support to the neurons › Several types known › Ex: Schwann, microglial

 Microglial cells › Scattered throughout CNS › Phagocytize bacteria or cellular debris  Oligodendrocytes › Along nerve fibers › Provide myelin sheath (made of a fatty substance called myelin) around axon in CNS  Schwann cells › Same as oligodendrocytes but in PNS

 Remember: It’s a cell!  Body of neuron › Cell Body – contains cell organelles › Dendrites- carry messages to cell body › Axons – carry messages away from cell body  Cell Structures › Large nucleus with easily seen nucleolus › Chromatophilic substance – similar to rough ER  Scattered throughout cytoplasm, membranous › Neurofibrils- help support cell shape

 Can be myelinated or unmyelinated  PNS › Schwann cells form myelin sheath › Nodes of Ranvier- small breaks in myelin sheath  CNS › Oligodendrocytes form myelin › Myelinated neurons form white matter › Unmyelinated neurons form gray matter

 Multipolar › Many small branched dendrites › One axon › Found in CNS  Bipolar › Two processes off of cell membrane (one axon and one dendrite) › Neurons in special sense organs  Unipolar › One process off of cell body (one axon) › Found throughout PNS

 Sensory (afferent) neurons › Have sensitive dendrites that are stimulated by changes in environment › Message is taken into CNS › Usually unipolar or sometimes bipolar  Interneurons › Transfer, direct, and process messages within CNS › Usually multipolar  Motor (efferent) neurons › Carries message out of CNS to effectors › Usually multipolar

 Inside the neuron › High in K + › High in negative ions  Outside the neuron › High in Na + › High in positive ions  Result › K + tends to diffuse out › Na + tends to diffuse in › Negative ions cannot cross

 Na/K pump - helps to restore concentration gradient across the cell membrane  Resting potential - difference is electrical charge across the membrane › Established by concentration gradients of various ions › Inside of the membrane has a negative charge of 70 mv › Membrane is said to be polarized

 Stimuli cause changes to the resting potential by making the inside of the membrane less negative  Once a stimulus happens: › If stimulus is not strong enough to reach threshold potential = cell membrane will return to resting potential › If stimulus is strong enough to reach threshold potential = start an action potential  Summation - when additive effect of stimuli causes action potential

 Starts at trigger zone of axon  Threshold stimulus open sodium channels  Sodium moves into axon › Because of the concentration gradient › Because of the negative charge that attracts the positive ions  Depolarizes the membrane as negative charge diminishes  Potassium channels open and potassium moves out of the axon, repolarizing the membrane  Animation #1 Animation #2 Animation #1Animation #2

Action Potential Animation

 Action potential at the trigger zone stimulates the next part of the axon to do a action potential  Potentials spread along the axon like a wave  Unmyelinated axons › Wave continues uninterrupted; relatively slow  Myelinated axons › Wave goes through saltatory conduction (jump from one node to the next); very fast Animation

 All-or-nothing effect › Neuron does not react until a threshold stimulus is applied, but once it is applied it reacts fully  Stimuli greater than threshold levels don’t change the size of the response but changes its frequency  Refractory period: › After a action potential › Brief period of time › The nerve cannot be stimulated again.

 The connection between two neurons  Don’t touch, separated by synaptic cleft  One-way communication between axon of presynaptic neuron and dendrite of postsynaptic neuron  Neurotransmitters are made in the synaptic knob of the axon, stored in synaptic vesicles, and cross the cleft when needed

 Excitatory Action: › A neurotransmitter that puts a neuron closer to an action potential (facilitation) or causes an action potential  Inhibitory Action: › A neurotransmitter that moves a neuron further away from an action potential  Response of neuron: › Responds according to the sum of all the neurotransmitters received at one time

 Acetylcholine  Monoamines – modified amino acids  Amino acids  Neuropeptides- short chains of amino acids  Depression: › Caused by the imbalances of neurotransmitters  Many drugs imitate neurotransmitters › Ex: Prozac, zoloft, alcohol, drugs, tobacco

 When an action potential reaches the end of an axon, Ca+ channels in the neuron open  Causes Ca+ to rush in › Cause the synaptic vesicles to fuse with the cell membrane › Release the neurotransmitters into the synaptic cleft  After binding, neurotransmitters will either: › Be destroyed in the synaptic cleft OR › Taken back in to surrounding neurons (reuptake)  Animation Animation

 Groups of highly interconnected neurons that work together in the CNS  Convergence › Axons from different parts of the nervous system connect to the same neuron combining their affects  Divergence › A message from one neuron is sent to many neurons at once; amplifies message

Convergence Divergence

 Nerves are made of bundled axons, called nerve fibers  Nerve fibers › Sensory (afferent)- carry messages to CNS › Motor (efferent)- carry messages from CNS to effectors  Nerves › Same definitions hold true › Most nerves contain both types of fibers and are called mixed nerves

 A nerve fiber (axon) is surrounded with endoneurium  Nerve fibers are bundled together and surrounded with perineurium to form a fascicle  Fascicles are bundled together and surrounded with epineurium to form a nerve

 Path that the message takes through the body  Includes: › Sensor › Sensory neuron › Interneuron › Motor neuron › Effector

 Simplest nerve pathway is a reflex  Reflexes without pain › Involve only sensory and motor neurons › Ex: knee-jerk reflex  Reflexes with pain › Involve interneurons in CNS › Ex: withdrawal reflex

 Central nervous system  Consists of brain and spinal cord  Made of both gray and white matter  Covered in meninges

 Cranial Bone  Dura mater › First layer; tough, fibrous connective tissue › Forms inner periosteum of cranial bone › Folds into the cranium in some places to form division walls in the brain  Arachnoid mater › Web-like membrane over CNS › Does not dip into crevices

 Subarachnoid space › Below arachnoid layer › Contains cerebrospinal fluid  Pia mater › Lower layer of meninges › Forms a tight covering over brain › Does dip into crevaces

 Same except: › Vertebrae bones - protection › Epidural space- filled with loose connective and adipose tissue › All other are the same

 Flows through ventricles (spaces in brain) in the subarachnoid space, and through the central canal of the spinal cord  Fluid is made by the choroid plexus

 Stretches from brain to intervertebral disk between first and second lumbar vertebrae  31 pairs of spinal nerves come of the cord  Gray matter core surrounded by white matter

 Responsible for communication between brain and body and spinal reflexes  Ascending tracts › Nerves that send info to brain  Descending tracts › Nerves that send into to effectors

 Made up off about 100 billion neurons  Four main sections: › 1) Cerebrum  Nerves for processing sensory and motor function  Higher functions (like reasoning) › 2) Diencephalon  Processes sensory information › 3) Brainstem  Regulates certain body functions like breathing › 4) Cerebellum  Coordinates skeletal muscle movements

 Divided into two hemispheres: right and left  Corpus callosum › Connects the two sides  Other structures › Convolutions - ridges › Sulcus - shallow groove › Fissure - deep groove

 Frontal lobe  Parietal lobe  Temporal lobe  Occipital lobe  Insula  Each lobe has unique functions

 Cerebral cortex › Thin layer of gray matter surrounding cerebral hemisphere; contain most of the cell bodies in the cerebrum  Inner part of the cerebrum is mainly made of white matter

 Motor areas › Primarily in frontal lobe › Send information out to effectors  Sensory areas › Interpret information from sensors › Area in parietal, temporal, and occipital lobes  Association areas › Analyze information from sensors › Located in areas in all lobes mentioned above

 Located between the cerebral hemispheres above the brainstem  Contains: › Thalamus › Hypothalamus › Pituitary gland › Pineal gland

 Thalamus › Routes sensory impulses to the correct region of the cerebrum  Hypothalamus › Monitors many internal conditions, link between nervous and endocrine system  Limbic system › Thalamus, hypothalamus, and basal nuclei › Controls experience and expression (feelings)

 Connection between spinal cord and the rest of the brain  Contains: › Midbrain › Pons › Medulla oblongata

 Located between diencephalon and pons  Contains some visual and auditory reflexs  Serves as the main connection for motor neurons between spinal cord and upper part of brain

 Rounded bulge between midbrain and medulla oblongata  Relays impulses between medulla and cerebrum or between cerebrum and cerebellum

 Lowest part of brain, connect to spinal cord  All ascending and descending tracts run through the oblongata  Serves as a control center for many vital function like heart rate, blood pressure, and respiratory center

 Located in the lower back part of the brain  Structured liked cerebrum with inner white matter core and gray matter covering  Controls posture and complex skeletal movements

 Peripheral Nervous system  Includes: › 12 pairs of cranial nerves › 31 pairs of spinal nerves  Divided into: › 1) Somatic nervous system  Controls conscious activities; connects to skin and skeletal muscles › 2) Autonomic nervous system  Controls unconscious activities; connects to internal organs or structures

 Two branches: › 1) Parasympathetic  Control under more normal conditions › 2) Sympathetic  Control under stress or emergency conditions (fight or flight)  Usually these have antagonistic effects › Work to counteract each other (one increases, while other decreases)  Either might be utilized to maintain homeostasis