BMC L1 Flashcards
Functions of Nervous System
Sensory input: Recieves / gathers info
Intergration: Nervous system processes recieved sensory info + decides what to do at each specific moment
Motor output: Nervous system activates effector organ to produce response
What problems could arrise if the nervous system started to function incorrectly?
Disease
Injuries
Develpment problems
Central Nervous System
Brain + Spinal Cord
Conctrol centre - computes + controls info
Intergration
Protected by BBB - Blood Brain Barrier
Brain is housed in + protected by cranial cavity
Spinal cord is protected by vertebrae
Choroid plexus: ventricles which produce CSF
Meninges: enclose on both sides of brain + spinal cord
Peripheral Nervous System
Nervous system that is not part of CNS. Nervous systen outside of CNS. All the nerves + ganglia outside of aCNS
Consists of spinal nerves + cranial nerves
Spinal nerves: carry impules from spinal cord
Cranial nerves carry impulses from brain
Allows communication between human body and CNS. Allows communication between organs + limbs and CNS
PNS not protected by BBB
PNS not protected by vertebrae / skull
PNS has two functional divisions:
-afferent division
-efferent division
Afferent / Sensory Division of PNS
Where nerve fibres (axons) which transmit impulses to froms sensory receptors to CNS.
Two types of these sensory receptors:
Somatic sensory fibres: transmit impulses from skin, skeletal muscles, joints
Visceral sensory fibres: transmit impulses from visceral organs to CNS
Effererent / Motor Division of PNS
Where nerve impulses transmit impulses from CNS to effector organs. This activates effectors to produce a response. For example, a muscle contracts or gland secretes hormone
Motor division of PNS also has two subdivisions:
Somatic Nervous Systsem
Autonomic Nervous System
Somatic Nervous System
Part of motor division of PNS that controls voluntary activity / movement (voluntary activity under conscious control)
Consists of somatic motor nerve fibres which send electrical impulses from CNS to skeletal muscles
Autonomic Nervous System
Part of motor division of PNS that controls involuntary activity / movement
Consists of visceral motor nerve fibres which regulate/control glands, smootg + cardiac muscle
The autonomic nervous system has two subdivisions:
Symathetic: Fight / Fright
Parasympathetic
Afferent
To carrry towards
Efferent
To carry away
Inputs
Travel from sensory recpetors to CNS via afferent nerves
Inputs
Travel from sensory recpetors to CNS via afferent nerves
Outputs
Travel from CNS to effectors via efferent nerves
Levels of organisation of Nervous System
DIAGRAM L1
Two types of cells which make up nervous tissue
- Glial cells / Neuglia: “Supporting cells”
Surround delicate nerve cells + suppory them - Neurones: Nerve cells which are excitable. This means that they can respond to stimuli by changing their membrane potentials. They can transmit electrical impulses
What are the two key neurotransmitters in the PNS?
- Noradrenaline
- Acetylcholine
What are the 2 types of tisssue that make up nervous system?
- Connective tissue
- Blood vessels
Describe the structure of a neurone
- Dendrites
- Axon
- Cell Body
- Nucleus
- Nucleolus
- Nissl Bodies
- Axon Hillock
- Axon Terminal
- Neurilemma
- Schwann Cell / One internode
- Node of Ranvier
- Terminal Branches
Function of dendrites
Dendrites recieve incoming signals/electrical impulses + carry them towards cell body. They are the receptive + input region.
Dendrites also increase the surface area for recieving incoming signals because there are many of them
Function of axons
Axons generate + transmit signals/electrical impulses + carry them away from cell body
Structure of dendrite
They are rough - due to dendritic spines
Can have ribosomes
Cannot have myelin
There are many dendrite
Branch near cell body
Structure of axons
They are smooth as no dendritic spines
No ribosomes
Can be myelintated
One axon
Branch further from cell body
Function of terminal branching
Forms junctions with other nerve cells
CNS vs PNS terminology
Nuclues: Bundle of neurones in CNS
Ganglion: Bundle of neurones in PNS
Tract: Bundle of axons in CNS
Nerve: Bundle of axons in PNS
Soma
Soma is nerve cell body
Consists of prominent nucleulus and nissl bodies
Organelles
- Cytosol: K+ reach solution inside cell, conataining enzymes for metabolism
- Nucleus: DNA maintence, RNA transcription, control of cell activities
- Nucleolus: Production of pre-ribosome
- Polyribosomes: Lots of free ribosomes attached to one strand of mRNA which produce multiple copies of same protein
- Mitochondria:
Production of energt from glucose substances. Also release adenosine triphosphate - Golgi Apparatus:
Processing, packaging, sorting + modifications of proteins - Rough ER:
Translation + folding of new proteins - Nissl bodies: Granules of rough ER. Unique to neurones. Have free ribosomes attached. Site of protein synthesis
Functional Classification of neurons
Classing neurons based on the direction they transmit electrical impulses relative to CNS
Sensory Neurones
Carry electrical impulses from sensory receptors to CNS
Soma not in CNS
Example of sensory receptors: Pressure receptors, pain recpetors, proprioreceptors
Motor Nuerones
Carry electrical impulses from CNS to effector organs
Soma in CNS
Somatic motor neurone involved in locomotion
Effector organs produce a response to stimulus when activated + include muscle + glands
Interneurones
Carry electrical impulses from sensory neurones to motor neurones
Full cell body in CNS
Sensory Neurone Structure
- Long dendrites, short axon
- Dendrite + cell body not in spinal cord but in dorsal root ganglia
Internuerone Structure
- Short dendrite, long/short axon
- Full cell body in CNS
Structural classifications of neurones
Neurones classified based on how many processes extend from the central body
Multipolar Neurones
Multiple processes
Many dendrites
One axon
Most common in humans
Allows for multiple connections
Mostly interneurones, some motor neurones
Bipolar Neurones
2 processes
Many dendrites
One axon
FUSED DENDRITES, DENDRITES FUSED WITH ACTIONS
RARE IN HUMANS
FOUND IN SENSORY ORGANS (SMELL, EYES, EARS, TASTE)
Most do not generate action potentials, those that do do not have a universal trigger point
All sensory neurones
Unipolar Neurones
1 Process
No denrites
One axon
Found in PNS, dorsal root ganglia, cranial nerve ganglia
1 SHORT SMALL PROCESS WITH 2 BRANCHES
BRANCH 1: Peripheral branch: Peripheral process (usually associated with sensory receptors)
Branch 2: Central Branch - Central process, branches into CNS
Mostly sensory neurones, some interneurones
3 Regions of Neurone
- Receptive region: recieves signal
- Conductive region: Transmits electrical impulse/signal
- Secretory region: secretes neurotransmitters
Neuroglia / Glial Cells
Supporting cells
6 types, 4 in CNS, 2 in PNS
Ependymal cells
- Found in chloroid plexi of ventricles
- Line the cerebospinal fluid-filled cavities
- Filter blood to produce CSF
- Seperate interstital fluid of fluid filled cavities
- Similar to epithelial cells, can have different shapes, can be squammus or columnar
- Can be cilliated
Oligodendrocytes
- Have processes which form myelin sheath around CNS nerve fibres
- Myelin sheath insulates neurone axons
- Oligodendrocytes have fewer processes than astrocytes
Astrocytes
- Most abundant glial cells in CNS
- Surround neurones, synaptic endings + capillaries
Function:
- Provide mechanical support
- Maintain neuronal spacing
- Guide migration of new neurones
- Control micro-chemical environment of brain
- Alter permeability of capillaries for ions
NOT BBB - Blood Brain Barrier - formed by tight junctions between epithelial cells of capillaries and basal membrane of capillary
Satellite cells
- Surround neurone cell bodies in PNS
- Functional equivalent of astrocytes in PNS
Schwann Cells
- Functional equivalent of oligodendrocytes in PNS
- Tightly wrap around neurones in PNS, and around the thicker neurones, they form myelin sheath
- One schwann cell = one internode
- Gaps between myelin sheath - nodes of ranvier, sites of ion exhange
- Schwann cells allow recognition of damaged nerve cells
Microglia
- Defensive cells in CNS
- Similar to macrophages
- Travel to injured neurones
- Phagocytises neuronal debris, microorganisms
This protection provided by microglia is very important as the immune system has limited access to the CNS
Myelin
- Fatty white substance which surrounds axons
- 70% lipid, 30% protein
- 30% protein is myelin basic protein (MBP)
- Myelinated axons are white, hence “white matter” in brain
Myelin surrounds long + large diameter axons:
- Protects
- Insulates
- Increases speed of signal
How do schwann cells form myelin sheath/ myelinate axon?
- Schwann cell ENVOLOPES axon
- Schwann cell then ROTATES around axon
- Plasma membrane of schwann cell then LOOSELY wrap around axon in succesive layers
- Cytoplasm of schwann cell forced between the two membranes
- These membranes wrapping tightly around axon forms myelin sheath
