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The Nervous System. Chapter 48-49. What you need to know!. The anatomy of a neuron. The mechanisms of impulse transmission in a neuron. The process that leads to release of neurotransmitter, and what happens at the synapse. The components of a reflex arc and how they work.

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The nervous system

The Nervous System

Chapter 48-49


What you need to know
What you need to know!

  • The anatomy of a neuron.

  • The mechanisms of impulse transmission in a neuron.

  • The process that leads to release of neurotransmitter, and what happens at the synapse.

  • The components of a reflex arc and how they work.

  • The organization and function of the major parts of the nervous system.

  • One function for each major brain region.

  • The location and function of several types of sensory receptors.

  • How skeletal muscle contracts.

  • Cellular events that lead to muscle contratction


The neuron
The Neuron

  • Functional unit of the nervous system

  • Dendrites: cell extensions that receive

    incoming messages from

    other cells

  • Axon: transmit messages to other cells

    • Covered in myelin sheath (Schwann cells or oligodendrocytes) to speed up transmission

  • Synapse: is the junction between axons and dendrites

  • Neurotransmitters (NT): chemical messengers (drugs) released from the synaptic terminals of the axon which bind to receptors of the receiver (another neuron, muscle cell, or gland)

    • Acetylcholine, dopamine, serotonin, GABA, etc.


Nervous system
Nervous System

  • Central nervous system (CNS) = brain & spinal cord

  • Peripheral nervous system (PNS) = everything else including motor and sensory neurons

  • Nerves are clusters of neurons

    Types of neurons:

  • Sensory receptors: receive information from the environment

  • Sensory neurons: send signals from receptors to CNS

  • Interneurons: brain and parts of the spinal cord

  • Motor neurons: transmit signals to effectors (muscles, glands)


Action potential nerve impulse
Action Potential (nerve impulse)

  • Membrane potential: difference in electrical charge across the cell membrane

  • Resting potential: neuron at rest (-70mV)


Action potential ap
Action Potential (AP)

  • All or none response to stimulus

  • If membrane potential reaches threshold (-55mV) AP will fire

  • Resting state

  • Depolarization

  • Depolarization >= threshold  AP

  • Repolarization

  • Undershoot


Axon

  • APs propagate down the axon

  • It jumps from one node of Ranvier to the next (saltatory conduction)

  • The signal is revitalized at every node

  • At the synapse the signal continues via electrical or chemical (NT) stimulus

    • Stimulus can be inhibitory or excitatory


Reflex arc
Reflex Arc

  • Simplest response to stimulus

  • Receptor  sensory neuron  interneuron (spinal cord)  motor neuron  effector (reaction)

  • The brain finds out later


Central nervous system
Central Nervous System

  • Brain and spinal cord

  • Cells bathed in cerebrospinal fluid (CSF) for nutrients and cleansing

  • Grey matter = neuron cell bodies and unmyelinated axons

  • White matter = myelinated axons

  • Neural glial cells (glia) support neurons:

    • Astrocytes provide nutrients for neurons

    • Oligodendrocytes make myelin sheath in the CNS (Schwann cells in the PNS)


Peripheral nervous system
Peripheral Nervous System

  • Divided into two subdivisions:

  • Somatic nervous system: muscles you control

  • Autonomic nervous system: automatic muscle and organ control subdivided into two more categories

    • Sympathetic division: fight or flight mechanism

    • Parasympathetic division: rest and digest


Brain
Brain

  • Compartmentalized:

  • Brainstem = medulla oblongata, pons, and midbrain

    • Primitive brain = primitive functions like homeostasisand breathing

  • Cerebellum: coordinated motor movement

  • Thalamus: main center for all sensory and motor information

  • Hypothalamus: regulates homeostasis and basic survival behaviors

  • Cerebrum: two hemispheres with grey over white matter

    • Cerebral cortex: Higher order thinking occurs here (largest in mammals) and voluntary movement

  • Corpus callosum: white matter enabling communications of the two hemispheres


Sensory receptors
Sensory Receptors

Perception: brain recognition of stimulus

Reception: receptor detects a stimulus

  • Mechanoreceptors: stimulated by physical stimuli

  • Thermoreceptors: stimulated by temperature

  • Chemoreceptors: chemical stimulation (taste and smell)

  • Electromagnetic receptors (photoreceptors): detect various forms of energy (light, electricity, or magnetism)

  • Pain receptors: detect too much heat or chemicals released from dying cells



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