Warm-Up Name the 2 main organs of the nervous system. Draw and label the parts of a neuron.

Warm-Up Label the parts of the neuron below. A B E F C G D

Warm-Up One neuron transmits a nerve impulse at 40 m/s. Another conducts at the rate of 1 m/s. Which neuron has a myelinated axon? List the following in order: K+ channels open and K+ floods out of cell Membrane is polarized (resting potential) Neurotransmitters are released from vesicles into synaptic cleft Na+ channels open and Na+ floods into cell Stimulus triggers membrane depolarization What restores the resting potential of a neuron?

The Nervous System

Nervous System Master controlling and communicating system

Basic Functions Sensory input – gather information Integration – process and interpret sensory input Motor output – response by muscles and glands

Organization Central Nervous System (CNS) Brain & spinal cord Integrative and control centers Peripheral Nervous System (PNS) Nerves (spinal nerves, cranial nerves) Communication lines between CNS and rest of body Two Divisions: Sensory (afferent) Division: Sensory receptors  CNS Motor (efferent) Division: CNS  effectors (muscles & glands)

Motor Division Somatic nervous system (voluntary) – control skeletal muscles Autonomic nervous system (ANS) (involuntary) – regulate smooth muscles, cardiac, glands Subdivisions: sympathetic & parasympathetic

Nervous Tissue Neurons (nerve cells) - transmit message Anatomy: Cell body – contains nucleus; metabolic center Dendrite – fiber that conveys messages toward cell body Axon – conduct nerve impulses away from the cell body Axon terminals – end of axon; contain neurotransmitters & release them Synaptic cleft/synapse – gap between neurons

Myelin: whitish, fatty material that covers nerve fibers to speed up nerve impulses Schwann cells: surround axons and form myelin sheath Myelin sheath: tight coil of wrapped membranes Nodes of Ranvier: gaps between Schwann cells

rotates around the axon, wrapping its plasma membrane loosely around Schwann cell plasma membrane Schwann cell cytoplasm A Schwann cell envelopes an axon. 1 Axon Schwann cell nucleus The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers. 2 Neurilemma The Schwann cell cytoplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath. 3 Myelin sheath (a) Myelination of a nerve fiber (axon) Figure 11.5a

Nervous Tissue Supporting cells Neuroglia CNS: astrocytes create the blood-brain barrier between capillaries and neurons microglia immune/defense ependymal cells line brain and spinal cord cavities and produce cerebrospinal fluid Oligodendrocytes wrap axons; produces myelin sheaths (covering) PNS: Schwann cells wrap axons; produces myelin sheaths (covering) satellite cells give support to neurons and regulate chemical environment

Classification of Neurons

Functional Classification: direction nerve impulse is traveling Sensory neurons Motor neurons Interneurons carry impulses from sensory receptors to CNS carry impulses from CNS to muscles & glands connect sensory & motor neurons Vision, hearing, equilibrium, taste, smell, pain, pressure, heat

Functional Classification: direction nerve impulse is traveling Sensory Neurons afferent most are unipolar some are bipolar Interneurons multipolar in CNS Motor Neurons efferent carry impulses to effectors, muscle or gland

Structural Classification: # processes extending from cell body Multipolar Bipolar Unipolar 1 axon, several dendrites 1 axon, 1 dendrite 1 process Most common (99%) Rare Short with 2 branches (sensory, CNS) Eg. Motor neurons, interneurons Eg. retina, nose, ear Eg. PNS ganglia

Structural Classification: # processes extending from cell body Multipolar neurons Bipolar Unipolar

Ganglia: collections of cell bodies Bundles of nerve fibers = tracts (CNS) or nerves (PNS) White matter: dense collections of myelinated fibers Gray matter: unmyelinated fibers & cell bodies

Neurotransmitters Neurotransmitter Action Affected by: Acetylcholine muscle contraction botulism, curare (paralytic), nicotine Dopamine “feeling good” cocaine, amphetamines Serotonin sleep, appetite, nausea, mood, migraines Prozac, LSD, ecstasy Endorphins inhibit pain morphine, heroin, methadone GABA main inhibitory NT alcohol, Valium, barbiturates

Protection of CNS Meninges: connective tissue covering CNS structures Dura mater (leathery outer), arachnoid mater (web-like middle), pia mater (surface of brain) Cerebrospinal fluid (CSF): watery cushion to protect NS from trauma

Blood-Brain Barrier: endothelial cells in capillaries prevent substances from crossing into brain NO: YES: Urea Toxins Proteins White blood cells Bacteria Most drugs Water Glucose Amino acids Gases Fat-soluble substances Some drugs: anesthetics, alcohol, nicotine

Skin of scalp Periosteum Bone of skull Dura Periosteal mater Meningeal Superior sagittal sinus Arachnoid mater Pia mater Subdural space Arachnoid villus Blood vessel Subarachnoid space Falx cerebri (in longitudinal fissure only) Figure 12.24

Right lateral ventricle (deep to cut) Superior sagittal sinus 4 Choroid plexus Arachnoid villus Interventricular foramen Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle 3 Third ventricle CSF is produced by the choroid plexus of each ventricle. 1 Cerebral aqueduct Lateral aperture Fourth ventricle CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. 2 Median aperture 2 Central canal of spinal cord CSF flows through the subarachnoid space. 3 (a) CSF circulation CSF is absorbed into the dural venous sinuses via the arachnoid villi. 4 Figure 12.26a

Label the parts of the neuron below using the following terms: axon terminal, cell body, dendrite, myelin sheath, node of Ranvier, nucleus of the neuron, Schwann cell nucleus. A B E F C G D