CNS v PNS
CNS v PNS
CNS - Central Nervous System
Brain and spinal cord enclosed by cranium and vertebral column
PNS - Peripheral Nervous System
All nervous system minue brain and spinal cord - mostly consists of nerves and ganglia
Ganglia - knot-like swelling in a nerve where neuron cell bodies are concentrated
contains sensory and motor divisions each with somatic and visceral subdivisions
Sensory (afferent) division: carries signals from receptors to CNS
Somatic sensory division: carries signals from receptors in the skin, muscles, bones, and joints
Visceral sensory division: carries signals from the viscera (heart, lungs, stomach, and urinary bladder)
Motor (efferent) division - carries signal from CNS to effectors (glands/muscles that carry out body’s response)
Visceral motor division (autonomic nervous system) - carries signal to glands, cardiac muscle, and smooth muscle
Involuntary responses are called visceral reflexes
Sympathetic division - arouse body reaction and speeds up processes
Parasympathetic division - slows body reactions down, stimulate digestion and urinary systems
Somatic motor division - carries signal to skeletal muscles
Output produces muscular contraction as well as somatic reflexes - involuntary muscle contractions
Neurons
Properties
Excitability - repsonse to stimuli
Conductiity
Secretion
When an electrical signal reaches the end of nerve fiber, the cell secretes a chemical neurotransmitter that influences the next cell
Functional classes of neurons
Sensory (afferent) neurons - detect stimuli and transmit information about them towards the CNS
Interneurons (association neurons) - lies entirely in CNS connecting motor and sensory pathways
Receive signals from many neurons and carry out integrative function (make decisions on response)
Motor (efferent) neuron - sends out signals to muscles and gland cells (effectors)
Structure
Soma - control center of neuron
single, centrally located nucleus w large nucleolus
Cytoplasm contains golgi, ER, mitochondria, lysosomes, cytoskeleton
Cytoskeleton has dense mesh of microtubules and neurofibrils (bundles of actin filaments) that compartmentalizes rough ER into dark-staining Nissl bodies
No centrioles, no mitosis
Dendrites - branches come off soma
Primary site for receiving signals from other neurons
More dendrites, more info
Provide precise pathways for reception and processing of info
Axon
Axon collateral - branches of axon - rapid conduction
Axoplasm
Axolemma - plasma membrane of axon
One axon per neuron
Myelin sheath
Distal end of axon has terminal arborization: extensive complex of fine branches
Synaptic knob (terminal button)—little swelling that forms a junction (synapse) with the next cell
Contains synaptic vesicles full of neurotransmitter
Multipolar neuron
One axon and multiple dendrites
Most common – most neurons in CNS
Bipolar neuron
One axon and one dendrite
Olfactory cells, retina, inner ear
Unipolar neuron
Single process leading away from soma
Sensory cells from skin and organs to spinal cord
Anaxonic neuron
Many dendrites but no axon
Retina, brain, and adrenal gland
Neuralgia (glial cells)
Function
Protect neurons and help them function
Bind neurons together and form framework for nervous tissue
If mature neuron is not in synaptic contact with another neuron, it is covered by glial cells
Prevents neurons from touching each other
Gives precision to conduction pathways
Types (CNS ONLY)
Oligodendrocytes
Form myelin sheaths in CNS that speed signal conduction
Arm-like processes wrap around nerve fibers
Ependymal cells
Line internal cavities of the brain; secrete and circulate cerebrospinal fluid (CSF)
Cuboidal epithelium with cilia on apical surface
Microglia
Wander through CNS looking for debris and damage
Develop from white blood cells (monocytes) and become concentrated in areas of damage
Astrocytes
- Most abundant glial cell in CNS, covering brain surface and most nonsynaptic regions of neurons in the gray matter
- Diverse functions:
Form supportive framework
Have extensions (perivascular feet) that contact blood capillaries and stimulate them to form a seal called the blood–brain barrier
Convert glucose to lactate and supply this to neurons
Secrete nerve growth factors
Communicate electrically with neurons
Regulate chemical composition of tissue fluid by absorbing excess neurotransmitters and ions
Astrocytosis or sclerosis—when neuron is damaged, astrocytes form hardened scar tissue and fill in space
Types (PNS ONLY)
Schwann cells
Envelope nerve fibers in PNS
Wind repeatedly around a nerve fiber
Produce a myelin sheath similar to the ones produced by oligodendrocytes in CNS
Assist in regeneration of damaged fibers
Satellite cells
Surround the neurosomas in ganglia of the PNS
Provide electrical insulation around the soma
Regulate the chemical environment of the neurons
CNS v PNS
CNS - Central Nervous System
Brain and spinal cord enclosed by cranium and vertebral column
PNS - Peripheral Nervous System
All nervous system minue brain and spinal cord - mostly consists of nerves and ganglia
Ganglia - knot-like swelling in a nerve where neuron cell bodies are concentrated
contains sensory and motor divisions each with somatic and visceral subdivisions
Sensory (afferent) division: carries signals from receptors to CNS
Somatic sensory division: carries signals from receptors in the skin, muscles, bones, and joints
Visceral sensory division: carries signals from the viscera (heart, lungs, stomach, and urinary bladder)
Motor (efferent) division - carries signal from CNS to effectors (glands/muscles that carry out body’s response)
Visceral motor division (autonomic nervous system) - carries signal to glands, cardiac muscle, and smooth muscle
Involuntary responses are called visceral reflexes
Sympathetic division - arouse body reaction and speeds up processes
Parasympathetic division - slows body reactions down, stimulate digestion and urinary systems
Somatic motor division - carries signal to skeletal muscles
Output produces muscular contraction as well as somatic reflexes - involuntary muscle contractions
Neurons
Properties
Excitability - repsonse to stimuli
Conductiity
Secretion
When an electrical signal reaches the end of nerve fiber, the cell secretes a chemical neurotransmitter that influences the next cell
Functional classes of neurons
Sensory (afferent) neurons - detect stimuli and transmit information about them towards the CNS
Interneurons (association neurons) - lies entirely in CNS connecting motor and sensory pathways
Receive signals from many neurons and carry out integrative function (make decisions on response)
Motor (efferent) neuron - sends out signals to muscles and gland cells (effectors)
Structure
Soma - control center of neuron
single, centrally located nucleus w large nucleolus
Cytoplasm contains golgi, ER, mitochondria, lysosomes, cytoskeleton
Cytoskeleton has dense mesh of microtubules and neurofibrils (bundles of actin filaments) that compartmentalizes rough ER into dark-staining Nissl bodies
No centrioles, no mitosis
Dendrites - branches come off soma
Primary site for receiving signals from other neurons
More dendrites, more info
Provide precise pathways for reception and processing of info
Axon
Axon collateral - branches of axon - rapid conduction
Axoplasm
Axolemma - plasma membrane of axon
One axon per neuron
Myelin sheath
Distal end of axon has terminal arborization: extensive complex of fine branches
Synaptic knob (terminal button)—little swelling that forms a junction (synapse) with the next cell
Contains synaptic vesicles full of neurotransmitter
Multipolar neuron
One axon and multiple dendrites
Most common – most neurons in CNS
Bipolar neuron
One axon and one dendrite
Olfactory cells, retina, inner ear
Unipolar neuron
Single process leading away from soma
Sensory cells from skin and organs to spinal cord
Anaxonic neuron
Many dendrites but no axon
Retina, brain, and adrenal gland
Neuralgia (glial cells)
Function
Protect neurons and help them function
Bind neurons together and form framework for nervous tissue
If mature neuron is not in synaptic contact with another neuron, it is covered by glial cells
Prevents neurons from touching each other
Gives precision to conduction pathways
Types (CNS ONLY)
Oligodendrocytes
Form myelin sheaths in CNS that speed signal conduction
Arm-like processes wrap around nerve fibers
Ependymal cells
Line internal cavities of the brain; secrete and circulate cerebrospinal fluid (CSF)
Cuboidal epithelium with cilia on apical surface
Microglia
Wander through CNS looking for debris and damage
Develop from white blood cells (monocytes) and become concentrated in areas of damage
Astrocytes
- Most abundant glial cell in CNS, covering brain surface and most nonsynaptic regions of neurons in the gray matter
- Diverse functions:
Form supportive framework
Have extensions (perivascular feet) that contact blood capillaries and stimulate them to form a seal called the blood–brain barrier
Convert glucose to lactate and supply this to neurons
Secrete nerve growth factors
Communicate electrically with neurons
Regulate chemical composition of tissue fluid by absorbing excess neurotransmitters and ions
Astrocytosis or sclerosis—when neuron is damaged, astrocytes form hardened scar tissue and fill in space
Types (PNS ONLY)
Schwann cells
Envelope nerve fibers in PNS
Wind repeatedly around a nerve fiber
Produce a myelin sheath similar to the ones produced by oligodendrocytes in CNS
Assist in regeneration of damaged fibers
Satellite cells
Surround the neurosomas in ganglia of the PNS
Provide electrical insulation around the soma
Regulate the chemical environment of the neurons