PNS: Multiple Levels of Organization Flashcards
Central Nervous System
the brain and spinal cord
-The brain can be divided into the brainstem and cerebral hemispheres and cerebellum
Peripheral Nervous System
The neurons or parts of neurons that exist outside of the CNS and connect the CNS to other tissues of the body.
-Cranial nerves, spinal nerves, sympathetic trunk, ganglia, and peripheral nerves
Autonomic Nervous System
the visceral motor components of the PNS that control smooth muscle, cardia muscle, and glands. The ANS has a parasympathetic and sympathetic division
Parasympathetic Division of ANS
Deals with vegetative functions and mechanisms that maintain tissue health and/or build internal resources.
-Active in an animal at rest.
Sympathetic Division of the ANS
Prepares individual to deal with stressful/threatening situations.
-Defend itself or flee
Enteric Nervous System
A network of sensory, motor, and secretory neurons located within the wall of the gastrointestinal tract.
Neurons
A bundle of axons with their surrounding connective tissue and blood vessels, traveling in the PNS.
Plexus
Mingling of nerves in which axons rearrange between nerves. Plexuses may have ganglia associated with them
Ganglion
a cluster of neuron cell bodies in the PNS
Nucleus
A cluster of neuron cell bodies in the CNS
Afferent
A sensory neuron or pathway carrying information to the CNS
Efferent
A motor neuron or pathway carrying information away from the CNS to control effectors
Effector
tissue or cell that generates the response in a nervous system pathway (muscle/gland)
Somatic
refers to skin and musculoskeletal structures (muscles, bones, joints, tendons)
Visceral
internal organs, blood vessels, glandular tissue
Nervous System Function
- Communication between tissues
- Integrate and process information from the environment and the body
- Control movement and Physiological processes
Path of motor response
Sensory (afferent) info –> CNS–> Process –> Effector tissue –> Motor response
- Sensory info detected by sensory neurons
- Info travels to CNS by nerves
- Processed by interconnected neuron network
- Motor neurons generate response via peripheral nerves and neurons that release hormones into circulation
Functional tissue of the nervous system
Neurons and glial cells
CNS: grey and white matter
PNS: ganglia and nerves
Grey matter and ganglia
contain neuron cell bodies and supporting glial cells
White matter and Nerves
Contain axons, supporting glial cells
Nerves: support connective tissue
Neurons function
- Detect broad range of information from the internal and external environment
- Process that information via networks of interconnected neurons
- Communicate with other body tissues to control movement and physiological functions
Characteristics of a neuron:
Dendrites: detect and receive information
Axon: carries an electrical signal (action potential) over a distance
-Many covered with lipid myelin sheath
Axon terminal: at the end of the axon branch which forms close contacts (synapses) with other neurons/effector cells
3 categories of neurons
- Multipolar
- Pseudounipolar
- Bipolar
Functional categories of neurons
Sensory
Motor
Interneurons
The Synapse
- Chemical synapses occur at regions of close contact between axon terminal and neuron/effector cell.
- Allows communication between cells
- Action potential –> synaptic vesicles release neurotransmitters and binds to receptors on post-synaptic membrane
- Binding of neurotransmitter alters the membrane potential of postsynaptic cell–> which may cause an action potential, muscle contraction, cell secretion…
Sensory (Afferent) Neurons
Detect and/or convey mechanical, chemical, and thermal changes in tissues or receptor organs they innervate.
-Special senses: Vision, hearing, vestibular, taste, smell
Sensory neurons innervate cutaneous, musculoskeletal and visceral tissues
- pseudounipolar neurons: carry sensory info from skin, muscle, bones, and viscera to CNS
- Sensory stimulation –> dendrite –> peripheral process (functions as an axon) –> Cell body –> Central process –> CNS
- cell body separation from main axon pathway allows action potential to travel to CNS without having to pass through cell body
Specialization of dendrites within tissue allow for detection of a variety of stimuli
- Nociceptors
- Mechanoreceptors
- Proprioceptors
Nociceptors
- Convey sensory information regarding tissue damage or the potential for damage
- Dendrites exists as free nerve endings
Mechanoreceptors
Detect tactile, pressure, and vibration type stimuli
Proprioceptors
detect stimuli related to body movement and position
Sensory Neurons for special senses
- Most are bipolar neurons
- Dendrites associated with specialized receptor cells
- Afferent neuron may function as the receptor
- Cell body may be in a ganglion
Interneurons
- Reside in the CNS and connect afferent and efferent neurons
- Interneurons are multipolar neurons
- Effect on other neurons may be excitatory or inhibitory
Motor (Efferent) Neurons
- Project to peripheral tissues and produce a response in those tissues
- Somatic and visceral efferent neurons
1. Somatic Motor
2. Visceral Motor
3. Neurosecretory
Somatic Motor Neurons
- Larger multipolar neurons
- Lower Motor Neurons: UMNs carry motor commands from the brain to LMNs in brainstem or spinal cord.
- LMN cell body is located in CNS– ventral horm of the spinal cord or in cranial nerve nucleus of brainstem.
LMN dendrites and cell body receive synaptic input from:
- UMN for voluntary movement and other movement requiring control by the brain
- Somatic afferents and local reflex circuits
neuromuscular junction
synapse formed with skeletal muscle fiber
Visceral Motor Neurons
- Multipolar neurons that innervate smooth muscle, cardiac, and glands
- Pathway from CNS to effector tissue involves 2 visceral motor neurons
- 1st cell body: in CNS
- 2nd cell body: peripheral ganglion
Neurosecretory Neurons
-Included in Motor section: contribute to output of nervous system
Spinal Cord
- Grey matter: contains neuron cell bodies and is shaped like a butterfly
- White matter: surrounds grey matter in spinal cord. Contains axons traveling into and out of spinal cord.
- Spinal cord is made of segments
- Spinal cord segments and spinal nerves: Cervical, Thoracic, Lumbar, Sacral, Caudal
Spinal Nerves
- Attached to the spinal cord by dorsal and ventral roots
- Dorsal root: contain sensory axons traveling to the spinal cord.
- Ventral root: contain motor axons leaving spinal cord
- Exit vertebral canal via intervertebral foramina which splits in 3 branches
1. Dorsal Branch
2. Ventral Branch
3. Communicating Branch
Vertebral Column
- The bony structure made up of the articulated vertebrae.
- Contain body and arch
- Vertebral bodies and arch
Spinal nerves exit the vertebral canal via..
Intervertebral foramina
Vertebral Formula of Dog/Cat
C7 T13 L7 S3 Cd ~20
Sympathetic Trunk
- Runs longitudinally along the ventrolateral aspect of vertebral bodies.
- Consists of axons and segmental ganglia from T1 to caudal spinal nerves
Autonomic ganglia
- Clusters of neurons located ventrolateral to vertebral bodies along sympathetic trunk.
- Connected to spinal nerves by communicating branches
- -Cranial cervical ganglion
- -Middle cervical ganglion
- -Cervicothoracic ganglion
Terminal ganglia
Microscopic clusters of neurons located within target tissue
