Nervous Tissue

Nervous System CNS (brain and spinal cord) CNS (brain and spinal cord) PNS (peripheral nervous system) PNS (peripheral nervous system)

Types of Cells Neurons – structural units Neurons – structural units Supporting cells – protect and myelinate neurons Supporting cells – protect and myelinate neurons

Structure of Neurons Cell body – contains nucleus and cytoplasm Cell body – contains nucleus and cytoplasm

Structure of Neuron Dendrites – receptive regions Dendrites – receptive regions

Structure of Neuron Axons – nerve impulse generators Axons – nerve impulse generators

Structure of Neuron Axoplasm – cytoplasm of neuron Axoplasm – cytoplasm of neuron

Structure of Neuron Axolema – plasma membrane Axolema – plasma membrane

Structure of Neuron Collaterals – axon branches Collaterals – axon branches

Structure of Neuron Axon hillock – an enlarged cell body structure, which is the beginning of the axon Axon hillock – an enlarged cell body structure, which is the beginning of the axon

Structure of Neuron Axon terminals – The axon and its collaterals end divide into fine processes Axon terminals – The axon and its collaterals end divide into fine processes

Structure of Neuron Synaptic end bulbs – tips of axon terminals that contain the synaptic vessicles Synaptic end bulbs – tips of axon terminals that contain the synaptic vessicles

Structure of Neuron Synaptic cleft – gap between two neurons Synaptic cleft – gap between two neurons

Structure of Neuron Supporting cells wrap themselves around the axons of some neurons like a jelly role Supporting cells wrap themselves around the axons of some neurons like a jelly role

Structure of Neuron Myelin sheath – A tight core of plasma membrane material around the axon Myelin sheath – A tight core of plasma membrane material around the axon

Structure of Neuron Neurilemma – The peripheral part of the schwann cell and the exposed plasma membrane Neurilemma – The peripheral part of the schwann cell and the exposed plasma membrane

Structure of Neuron Nodes of Ranvier – Since the myelin sheath is composed of several schwann cells there are gaps or indentations called nodes of ranier Nodes of Ranvier – Since the myelin sheath is composed of several schwann cells there are gaps or indentations called nodes of ranier

Classification by Structure 1. Unipolar 2. Bipolar 3. Multipolar

Unipolar Have only one process that extends from the cell body Have only one process that extends from the cell body

Unipolar Conduct impulses toward the CNS Conduct impulses toward the CNS

Bipolar Have two processes that extend from the cell body (one axon and one dendrite) Have two processes that extend from the cell body (one axon and one dendrite)

Bipolar Found in the eye, ear, and olfactory mucosa Found in the eye, ear, and olfactory mucosa

Multipolar Have several processes that extend from the cell body (several dendrites and one axon) Have several processes that extend from the cell body (several dendrites and one axon)

Multipolar Most neurons in CNS and neurons that carry impulses away from the CNS Most neurons in CNS and neurons that carry impulses away from the CNS

Classification by Function 1. Sensory 2. Motor

Sensory or Afferent Neurons Carry impulses away from sensory receptors in the skin, skeletal muscle, and internal organs. Carry impulses away from sensory receptors in the skin, skeletal muscle, and internal organs.

Sensory or Afferent Neurons Most are unipolar Most are unipolar

Sensory or Afferent Neurons Cell bodies lie outside the CNS Cell bodies lie outside the CNS

Motor or Efferent Neurons Carry impulses away from the CNS Carry impulses away from the CNS

Motor or Efferent Neurons Most are multipolar Most are multipolar

Motor or Efferent Neurons Cell bodies lie within the CNS Cell bodies lie within the CNS

Neuroglia Supporting cells Supporting cells

Neuroglia Half the volume in the CNS Half the volume in the CNS

Neuroglia Smaller than neurons Smaller than neurons

Neuroglia Five to fifty times more numerous Five to fifty times more numerous

Neuroglia Can divide Can divide

Neuroglia Do not generate or propogate action potentials Do not generate or propogate action potentials

Brain Tumors Derived from glia called gliomas Derived from glia called gliomas Highly malignant Highly malignant Grow fast Grow fast

Myelin sheath Some axons are covered by a myelin sheath produced by neuroglia Some axons are covered by a myelin sheath produced by neuroglia

Myelin sheath Increases speed of nerve impulse production Increases speed of nerve impulse production

Neuroglia Two types of neuroglia produce myelin sheath Two types of neuroglia produce myelin sheath 1. Schwann cells (PNS) 2. Oligodendrocytes (CNS)

Schwann Cells Helps in regeneration of PNS axons Helps in regeneration of PNS axons

Oligodendrocytes Inhibits axon regrowth after injury Inhibits axon regrowth after injury

Gray and White Matter In the brain and spinal cord some parts appear gray while other appear white In the brain and spinal cord some parts appear gray while other appear white

White Matter Contains the myelinated and unmyelinated axons of neurons Contains the myelinated and unmyelinated axons of neurons

Gray Matter Contains cell bodies, dendrites, and unmyelinated axons of neurons Contains cell bodies, dendrites, and unmyelinated axons of neurons Also contains neuroglia Also contains neuroglia

Organization of Nervous System 1. CNS 2. PNS

Organization of Nervous System PNS Somatic nervous system Somatic nervous system Autonomic nervous system Autonomic nervous system

Somatic Nervous System 1. Sensory neurons convey information from receptors in the body wall, limbs, head, and special senses

Somatic Nervous System 2. Motor neurons conduct impulses to skeletal muscles

Autonomic Nervous System 1. Sensory Neurons convey information from organs such as the lungs and stomach to the CNS

Autonomic Nervous System 2. Motor Neurons conduct impulses from the CNS to smooth muscle, cardiac muscle, and glands

Autonomic Nervous System The motor part can be subdivided further into the sympathetic and parasympathetic divisions The motor part can be subdivided further into the sympathetic and parasympathetic divisions

Synapses The functional junction between a neuron and an effector or between two neurons. The functional junction between a neuron and an effector or between two neurons.

Synapses Presynaptic neuron – The neuron sending the signal Presynaptic neuron – The neuron sending the signal

Synapses Postsynaptic neuron – the neuron receiving the message Postsynaptic neuron – the neuron receiving the message

Types of Synapses 1. Electrical 2. Chemical

Electrical Synapses Action potentials or nerve impulses are conducted directly between adjacent cells through gap junctions. Action potentials or nerve impulses are conducted directly between adjacent cells through gap junctions.

Electrical Synapses Ions flow from one cell to the next through the connexons thus the action potential is spread from one cell to the next. Ions flow from one cell to the next through the connexons thus the action potential is spread from one cell to the next.

Chemical Synapses Nerve impulses cannot be conducted across the synaptic cleft Nerve impulses cannot be conducted across the synaptic cleft

Chemical Synapses - Summary The presynaptic neuron converts an electrical signal (nerve impulse) into a chemical signal (neurotransmitter release). The presynaptic neuron converts an electrical signal (nerve impulse) into a chemical signal (neurotransmitter release).

Chemical Synapses - Summary Then the postsynaptic neuron converts the chemical signal back into an electrical signal (postsynaptic potential). Then the postsynaptic neuron converts the chemical signal back into an electrical signal (postsynaptic potential).

Chemical Synapses – 7 Steps 1. An action potential arrives at a synaptic end bulb of a presynaptic neuron

Chemical Synapses – 7 Steps 2. Voltage-gated calcium channels open and calcium flows into the synaptic end bulb of the presynaptic neuron

Chemical Synapses – 7 Steps 3. The increase in calcium concentration inside the synaptic end bulb signals the synaptic vessicles to release the neurotransmitters via exocytosis into the synaptic cleft

Chemical Synapses – 7 Steps 4. The neurotransmitters bind to receptors on the postynaptic neuron

Chemical Synapses – 7 Steps 5. Once the neurotransmitters bind to the receptors, ions flow across the membrane

Chemical Synapses – 7 Steps 6. As the ions flow across the membrane the voltage across the membrane changes (postsynaptic potential)

Chemical Synapses – 7 steps If sodium flows across the membrane it causes depolarization If sodium flows across the membrane it causes depolarization

Chemical Synapses – 7 steps If chlorine flows across the membrane it causes hyperpolarization If chlorine flows across the membrane it causes hyperpolarization

Chemical Synapses – 7 steps 7. Once a depolarizing postsynaptic potential reaches threshold, an action potential is triggered

Chemical Synapses Synaptic delay – The length of time between the arrival of the action potential at a presynaptic axon terminal and the membrane potential change on the postsynaptic membrane. Synaptic delay – The length of time between the arrival of the action potential at a presynaptic axon terminal and the membrane potential change on the postsynaptic membrane.

Chemical Synapses Due to the synaptic delay electrical synapses are faster than chemical synapses Due to the synaptic delay electrical synapses are faster than chemical synapses

Excitatory postsynaptic potential Depolarizing postsynaptic potential caused by the influx of sodium, potassium, and calcium Depolarizing postsynaptic potential caused by the influx of sodium, potassium, and calcium

Excitatory postsynaptic potential Once it reaches threshold an action potential is triggered Once it reaches threshold an action potential is triggered

Inhibitory postsynaptic potential A hyperpolarizing postsynaptic potential caused by the influx of chlorine or efflux of potassium A hyperpolarizing postsynaptic potential caused by the influx of chlorine or efflux of potassium

Inhibitory postsynaptic potential Makes it difficult for the generation of an action potential Makes it difficult for the generation of an action potential

Neurotransmitters 1. Small-Molecule Neurotransmitters 2. Neuropeptides

Small-Molecule Neurotransmitters 1. Acetylcholine  Released by PNS and CNS neurons  Can act as an excitatory (neuromuscular junction) or inhibitory neuron (heart)

Small-Molecule Neurotransmitters 2. Amino acid  CNS  Glutamate has excitatory effects (important for memory)  Gamma aminobutyric (GABA) has inhibitory effects

Small-Molecule Neurotransmitters 3. Biogenic amines  Amino acids that are modified and decarboxylated  Can be inhibitory or excitatory depending on the receptor  Norepinephrine, epinephrine, dopamine, and serotonin

Small-Molecule Neurotransmitters 3. Biogenic Amines continued  NE and Epinephrine play roles in arousal, dreaming, and regulating mood

Small Molecule-Neurotransmitters 3. Biogenic Amines continued  Dopamine are active during emotional responses, addictive behaviors, and pleasurable experiences

Small Molecule-Neurotransmitters 3. Biogenic Amines continued  Serotonin involved in sensory reception, temperature regulation, control of mood, appetite, and the induction of sleep

Parkinson disease Due to degeneration of neurons that release dopamine Due to degeneration of neurons that release dopamine

Schizophrenia Due to accumulation of excess dopamine Due to accumulation of excess dopamine

Small-Molecule Neurotransmitters 4. ATP and other Purines  CNS and PNS  Excitatory  Usually released with another neurotransmitter

Small-Molecule Neurotransmitters 5. Nitric Oxide  Simple gas  Plays a role in memory and learning  Causes vasodilation

Viagra Enhances the effect of NO Enhances the effect of NO

Neuropeptides 3-40 amino acids linked by peptide bonds 3-40 amino acids linked by peptide bonds CNS and PNS CNS and PNS Excitatory and Inhibitory actions Excitatory and Inhibitory actions Substance P enhances pain Substance P enhances pain Enkephalins and Endorphins inhibit pain (also morphine and heroin receptors) Enkephalins and Endorphins inhibit pain (also morphine and heroin receptors)