Week 4: Intro to the Nervous System Flashcards
Central Nervous System (CNS):
- Brain
- Spinal Cords
- Lined Meninges
Surrounded by cerebrospinal fluid (CSF)
Peripheral Nervous System (PNS):
- All nervous tissue outside of the CNS e.g.
- (most) cranial/spinal nerves
- Ganglia (groups of nerve cell bodies)
- Nerve endings (innervating tissues and organs)
Most cranial/spinal nerves (are myelinated by oligodendrocytes)
Functional Organization of the Nervous Systems:
- CNS: Brain, Spinal Cord
- PNS:
- Sensory: Afferent PNS - CNS division (Somatic sensory, visceral sensory)
Motor: Efferent CNS - PNS division (somatic (voluntary), Autonomic (involuntary) (sympathetic + parasympathetic)
Sensory (afferent):
Information coming in from PNS to be processed in the CNS
- Has somatic subdivision: Carries sensory information from skin, fascia, joints, skeletal muscles and special sense to the CNS for integration/processing
- Has visceral subdivision: Carries sensory information from internal organs to the CNS for integration/processing
Things you feel going through CNS to be processed e.g. pinching, bumping arm, mechanoreceptors, nociceptors
Motor (efferent):
- Information going out from CNS to effectors in the PNS
- Has somatic subdivision: Carries motor information from the CNS to skeletal muscle e.g. controls all body movements that we are aware of and can consciously influence
Has Autonomic (visceral) subdivision: Carries motor information from the CNS to cardiac muscle, smooth muscle and glands e.g. controls all motor impulses to muscles/glands that we cannot consciously influence
- Has somatic subdivision: Carries motor information from the CNS to skeletal muscle e.g. controls all body movements that we are aware of and can consciously influence
Overview of Peripheral Nerves:
PNS Nerve > inside out:
Neuron/nerve cell (wrapped in endoneurium, which is superficial to any myelin present)
bundled together
Fascicle (wrapped in perineurium)
bundled together
Nerve (wrapped in epineurium)
Myelin sheath is wrapped by Schwann cell
Structure of Spinal Nerves:
- Anterior/ventral roots contain motor neurons (information going out from CNS to PNS > effector muscles)
- Posterior/dorsal roots contain sensory neurons (information coming from PNS (sensory receptors) to CNS)
- Spinal nerves from where the anterior and posterior roots come together as they exit the spinal cord (both motor and sensory neurons)
- Either use anterior or posterior, Ventral or dorsal
- Also called horns. Only a spinal nerve when the two roots join as it carries motor and sensory and roots only carry on or the other
Once in becomes a spinal nerve it splits again - The spinal nerves then branch into anterior and posterior rami
- Posterior ramus: Taks motor input to and receives sensory input from the posterior structures of the body
- Anterior ramus: Takes motor input to and receives sensory input from the anterior structures of the body
All sources refer to it as a spinal nerve (don’t refer to the rami (ramus) but anatomically the correct term are rami) as it is often just referred to as the rami
Spinal Nerve Positioning:
- Spinal nerves exit the vertebral column in line with their vertebral counterpart
- Cervical nerves (C1-C7) exit above their corresponding vertebrae, while C8 exits below the seventh and final cervical vertebra
- Thoracis nerves T1-T12 exit below their corresponding vertebrae
- Spinal cord ends at approximately lumbar nerve L1, and from there nerves for a tail called Cauda Equina
- Lumbar nerves L1-L5 exit below their corresponding vertebrae
- Sacral nerves S1-S5 exit through the sacral foramina
- Spinal cord sits in the vertebral canal
- Holes next to vertebrae is the vertebra foramen which is where the spinal nerves come out
- Lumbar - variation among people, it is no longer thick, it is spaghetti called cauda equina and the spinal nerves either come out at the lumbar, or if its sacral it comes out the sacral foramina
Spinal tap/lumbar puncture is in the L1-L4 as it is softer and harder to hit the spinal cord (like poking spaghetti with a fork)
Peripheral Nerve Branches:
A typical nerve will have branches to simultaneously supply:
- Skin (cutaneous branch)
- Skeletal muscle (muscular branch)
- Blood vessels (vascular branch)
Joints (articular branch)
Each branch have both motor and sensory fibers present (information going both ways PNS > CNS)
- E.g. a nerve with a branch to a skeletal muscle has:
- Somatic (efferent) motor fibers controlling contraction of the muscle
- Somatic (afferent) sensory fibers feeding sensory information e.g. pain/stretch) back to the CNS
Autonomic efferent motor fibers controlling smooth muscle of the blood vessels that are located within the muscles
Sensory and Motor Neurons
- Sensory: Collects and receives information from somatic or visceral systems, may be afferent
- Interneurons: Processes, interprets and responds to information collected
Motor: Instructs and commands on somatic or visceral systems, also referred to as efferent
- Interneurons: Processes, interprets and responds to information collected
Neuron Interactions:
- Neurons interactions: Has two processes which extend form the cell body, dendrites and axons. These processes are known as nerve fibers which are long processes of neurons
A nerve is a collection of nerve fibers
Nerve cells:
- Neurons transmit impulses along a nerve fiber in one direction CNS- PNS/PNS-CNS
- Schwann cells: protect the axon, found in the PNS, may wrap many times around the axon, forms the myelin sheath
- Oligodendrocytes: Protect axon, found in CNS, may wrap many times around the axon, forms myelin sheath
- Neuroglia: small cells that outnumber neurons and play a role in support, nourishment and protection of neurons
- If nerve fibers have a myelin sheath it is myelinated. Allows faster transmission of axon potentials. Axons can be imbedded in a Schwann cell rather than it being wrapped around it
If an axon is not wrapped by a Schwann cell, it is unmyelinated and the action potentials will be slower
Peripheral Nervous System and its Branches:
- Muscular Branch: Somatic efferent motor fibers, somatic afferent sensory fibers, visceral efferent motor fibers
- Cutaneous Branch: Somatic afferent sensory fibers, visceral efferent motor fibers
Afferent and Efferent:
Afferent: Information carried towards the CNS from a receptor (sensory)
Efferent: Information carried away from the CNS to the target organ (motor)
Neural pathways:
- Ascending or descending
Neurons normally transmit impulses in one direction only
Naming of neural pathways:
- Neural tracts are usually named according to the origin and destination of the signal being transmitted along nerve fibers
Tract: the part of the pathway that is found within the CNS
Cells of the nervous system:
- Neurons: excitable nerve cells that communicated by electrical and chemical signals
Neuroglia: smaller supporting cells that surround or connect to neurons
Structure of a neuron:
Processes: projections extending from/to the cell body
Dendrites: Act as the main receptive input/region, provide a large surface area for receiving signals, forward incoming messages to the cell body
Axons: Arise from the cell body at the axon hillock and form a long slender process, are the conducting region of the neuron and transmits impulses away from the cell body, distal ending is called the axon terminal
Neurons send nerve impulses over the long distances by generating and conducting action potentials (AP) along their axons. The AP is sent along the axons entire length from its point of origin toward the axon terminal. The speed of transmission is affected by its degree of myelination
Functional types of neurons:
Sensory Neurons
Afferent: Receive information: Somatic, Autonomic
Motor Neurons: Efferent, convey information: Somatic (voluntary), Autonomic (involuntary)
Interneurons: Connect one neuron to another (CNS only)
Function of Somatic Sensory Neurons:
Receive information from sensory receptors and transmit to the CNS
Which of the following statements regarding the nervous control of muscles is CORRECT?
Skeletal muscle is under voluntary control by the motor neurons of the somatic nervous system
Which of the following statements explains why we are able to feel when someone squeezes our hand?
Somatic sensory neurons convey information from the PNS to be processed in the CNS
Nerve impulses are detected/received by which part of the neuron?
Dendrites
Neurons can be structurally classified as:
Unipolar, bipolar and multipolar
