Nervous System
Neuron Classifications
Sensory Neuron: Carries info from a receptor to the CNS
Motor Neuron: Carries commands to effectors
Interneuron: Located in the CNS (reflex center)
Connective Tissue Coverings
Perineurium: Covering around nerve bundles
Endonuerium: Covering around individual nerve fibers (Axons)
Epineurium: Outer covering of a nerve
Multipolar Neurons: Has many dendrites and an axon rising form the cell body: Most neurons with cell bodies in the CNS are multipolar.
Bipolar Neurons:
Unipolar Neurons :
Major Functions of the nervous system:
Integrative function: Coordination of sensory info in the CNS; this info helps decision making
Sensory function: Provided by sensory receptors, which detect internal or external change; info travels from receptors to sensory neurons
Motor function: Nerve impulses conduct along motor neurons to the effectors
Effectors: Muscles/glands that respond to nerve impulses
Tissues
Neuroglia: Cells that support neurons through nourishment, protection, and insulation
Neurons: Cells that communicate through electrical impulses
Axon:Conducts impulses away from the cell body
Axon Hillock: Thickening extension that rises from the cell body
Dendrites: Conduct impulses toward the cell body and provide a receptive service for communication with other neurons
Myelin Sheath: Increases the conduction speed of nerve impulses
Cell Body: Contains major organelles such as the nucleus
Ependymal Cells: Produces cerebrospinal fluid in the CNS
Oligodendrocytes: forms the myelin sheath around axons in the brain and spinal cord
Astrocyte: Lies between blood vessels and neurons
Microglia: Function as phagocytes for bacterial cells and cellular debris, and produces scar tissue
BRAIN
SPINAL CORD
Function
Structure
Spinal cord: Consists of 31 segments that each of which connect to a pair spinal nerves
Lumbar enlargement: A thickened area near the bottom of the spinal cord that provides nerves to the lower limbs
Ascending Tract: Carries sensory info to the brain
Descending Tract: Carries motor info from the brain to muscles or glands
Major Functions: transmit impulses to and from the brain, and house spinal reflex
Cervical enlargement: A thickened area near the top of the spinal cord that provides nerves to the upper limbs
White matter: Made of bundles of myelinated fibers, surrounds a core of grey matter that provides housing to interneurons and neuron cell bodies
Cuada Equina: structure formed near the end of the spinal cord; consists of spinal nerves in lumbar and sacral area
Dorsal root ganglia: Home to the cell bodies of sensory neurons that enter the spinal cord
Posterior and anterior horns: The upper and lower wings of grey matter
Lateral horn: lies between the posterior and anterior horns
Central canal: Contains cerebrospinal fluid and is located in the middle of the gray matter
Spinal Reflexes: Controlled by reflex arcs that pass through the spinal cord
REFLEX ARC
Interneuron: Carries info from sensory neurons to motor neurons
Motor Neuron: Carries info form brain/spinal cord out to an effector
Sensory Neuron: Carries info from a receptor toward the CNS
Effector: Responds to stimulation form a motor neuron and produces a reflex or behavioral action
Sensory Receptor: Detects changes
NEUROTRANSMITTERS: A chemical used to accomplish communication
- released in response to a nerve impulse
- more than 100 neurotransmitters exist within the human body
- composed of acetylcholine, amino acids, and neuropeptides
ACTION POTENTIAL AND THE NERVE IMPULSE
- Potassium channels on the axon open
- Potassium diffuses outward and repolarizes the axon membrane
- Sodium diffuses inward and depolarizes the axon membrane
- The action potential causes a local electric current that stimulates adjacent portions of the axon membrane
- Sodium Channels on the axon open
- A series of action potential occurs along the axon
- Stimulus is received
- Neuron maintains resting potential
AUTONOMIC NERVOUS SYSTEM
Parasympathetic divisions: Activates under regular, restful conditions(rest and digest).
Sympathetic division: Activates under stressful conditions or in emergencies(fight or flight).
MAJOR DIVISIONS AND SUBDIVISIONS OF THE NERVOUS SYSTEM
PERIPHERAL NERVOUS SYSTEM
CENTRAL NERVOUS SYSTEM
- Responsible for integration of info and decision making
- Made up of the brain and spinal cord
- Contains sensory and motor divisions
MOTOR FUNCTIONS
- Made up of cranial and spinal nerves that connect the CNS to the rest of the body
Autonomic nervous system: Controls involuntary effectors
Somatic nervous system: Controls voluntary skeletal muscles
Cerebellum: Coordinates muscular activity
Diencephalon : Processes sensory input and controls may homeostatic processes
Brainstem: Coordinates and regulates visceral activities, and connects different parts of the nervous system
Cerebrum: Largest part of the brain; associated with higher brain function, and sensory and motor functions
CRANIAL NERVES
- The first pair arises from the cerebrum, and the second from the thalamus, but most arise from the brainstem
- Most are mixed nerves, containing sensory and motor nerve fibers, but some are only sensory, while others are primarily motor
- The twelve pairs are designated by name and number; the numbers are in order, from superior to inferior
- There are twelve pairs of cranial nerves that arise from the underside of the brain
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