| The functions of the nervous system | Collect sensory input
Motor output
major controlling regulating and communicating system of the body
Fast acting and chemical and electrical signals
Center of all mental activity including thought learning and memory
Keeps us in touch with our environment external and internal |
| Collect sensory input | Sensory receptors means to obtain information about internal and external changes
Integration of input
Interpretation of sensory input to determine response to it |
| Motor output | Activation of effector organs (muscles and glands) produce is a response |
| Central nervous system (CNS) | 1. Brain
2. Spinal cord
Integration and command center |
| Peripheral nervous system (PNS) | 1. Paired spinal nerves attached a spinal cord
2. Paired cranial nerves attached to brain
Carry messages to and from the CNS
Multiple divisions |
| PNS functional divisions | Sensory (afferent) division
Motor (efferent) division |
| Sensory division (afferent) | Somatic afferent fibers
-convey impulses from skin, skeletal muscles, and joints
Visceral afferent fibers
-Convey impulses from visceral organs |
| Motor division (efferent) | Transmits impulses from CNS to effector organs |
| Motor divisions of PNS | Somatic nervous system (voluntary)
Autonomic nervous system (involuntary) |
| Somatic nervous system (voluntary) | Conscious control of skeletal muscle |
| Autonomic nervous system (Involuntary) | Visceral motor nerve fibers
Regulate smooth muscle, cardiac muscles and glands
To functional subdivisions:
-Sympathetic (fight or flight)
-Parasympathetic (Rest and digest) |
| Histology of nervous tissue | Very tightly packed cells
To principal cell types:
-Neurons
-Neuroglia (glial cells) |
| Neurons | Excitable cells that transmit electrical signals |
| Neuroglia | Smaller supporting cells with various functions |
| Cells of the CNS | Astrocytes
Microglia
Ependymal cells
Oligodendrocytes |
| Cells of the PNS | Satellite cells
Schwann cells |
| Neurons special characteristics | Long lived (100 years or more)
Amitotic
High metabolic rate (requires continuous supply of oxygen and glucose)
Plasma membrane functions in:
-electrical signaling
-Cell to cell interactions during development |
| Cell body (soma) | -Biosynthetic center of neurons with nucleus and organelles
-well developed Golgi apparatus
-rough ER called nissi bodies
-network of neurofibrils
-axon hillock: call shaped area with axon arises (determining place)
-clusters of cell bodies nuclei and ganglia |
| Clusters of cell bodies in the CNS | Nuclei |
| Clusters of cell bodies in the PNS | Ganglia |
| Dendrites | -Short, tapering and diffusely branched
-receptive region of neuron
-Convey electrical signals (graded potentials) toward cell body |
| Axon | -One axon per cell arising from axon hillock
-Long axons (nerve fibers)
-conducting region: generate and transmit nerve impulses (action potentials) away from soma |
| Bundle of nerve processes in the PNS | Nerve |
| Bundle of nerve processes in the CNS | Tract |
| Axon collaterals | Occasional branches |
| Telodendria | Numerous terminal branches |
| Synaptic knobs/Boutons/Axon terminals | Secretary region of neuron
Release neurotransmitters to excite or inhibit other cells |
| Anterograde | Toward axon terminal |
| Retrograde | Toward the cell body |
| Astrocytes | -Most abundant, versatile, and highly branched glial cells
-Cling to neurons, synaptic endings, and capillaries
Functions:
-Support and brace neurons
-Help determine capillary permeability
-Guide migration of young neurons
-Control the chemical environment
-Participate in information processing in the brain |
| Microglia | -Small, Ovid cells with thorny processes
-Migrate toward injured neurons
-Phagocytize microorganisms and neuronal debris
-defensive cells in CNS
Halloween cells eat up debris |
| Ependymal cells | -Range in shape from squamous to columnar
-May be ciliated
-Line the central cavities of the brain and spinal column
-Separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities |
| Oligodendrocytes | -Branched cells
-Processes wrap CNS nerve fibers, forming insulating myelin sheaths |
| Satellite cells | Surround and support neuron cell bodies in PNS |
| Schwann cells | -Surround peripheral nerve fibers and form myelin sheaths
-Vital to regeneration of damage peripheral nerve fibers |
| Myelin sheath | -Segmented protein lipoid sheath around most long or large diameter axons
Functions to:
-Protect an electrically insulate the axon
-Increase speed of nerve impulse transmission |
| Myelin sheaths in PNS | -Schwann cells rap many times around the axon
-Myelin sheath- Concentric layers of Schwann cell membrane
-Neurilemma-Peripheral bulge of Schwann cell cytoplasm |
| Nodes of Ranvier | -Myelin sheath gaps between adjacent Schwann cells
-Sites were axon collaterals can emerge |
| Unmyelinated axons | -Thin nerve fibers unmyelinated
-One Schwann cell may incompletely enclosed 15 or more unmyelinated axons |
| Myelin sheaths in CNS | -Form by processes of oligodendrocytes not the whole cells
-Nodes of Ranvier are present
-No neurilemma
-thinnest fibers are unmyelinated |
| White matter | Dense collections of myelinated fibers |
| Gray matter | Mostly neuron cell bodies and unmyelinated fibers |
| Functional classification of neurons | sensory
Motor
Interneurons |
| Sensory (afferent) | Transmits impulses from sensory Receptors towards CNS |
| Motor (efferent) | Carry impulses from CNS to effectors |
| Interneurons (Association neurons) | Shuttle signals through CNS pathways most entirely within CNS |
| Structural classification of neurons | Multipolar
Bipolar
Unipolar |
| Multipolar | One axon and several dendrites
Most abundant
Motor neurons and interneurons |
| Bipolar | One axon and one dendrite |
| Unipolar | Single, short process that has two branches
Peripheral process- More distal branch, often associated with a sensory receptor
Central process- branch Entering the CNS |
