Wk 4: Nervous System Flashcards
The central nervous system includes:
the brain and spinal cord
The peripheral nervous system includes:
nerves (cranial + spinal) and autonomic ganglia
What does the central nervous system do?
The control uni, performing integration and analysis of info and then signal/command as a response
What does the Peripheral nervous system do?
Relays information from internal environement and external environment to CNS then includes efferent responses from brain to target cells/organs
What are the 2 categories of the autonomic nervous system?
- Parasympathetic
- Sympathetic
Neurons
Excitable cells able to transmit nervous message-function will vary according to the type of neurons
Sensory neurons
Pseudo-unipolar, bipolar
transmit impulses towards CNS for processing
Interneurons
multipolar
Lie between motor & sensory neurons and shuttle signals through CNS pathways (99% of body’s neurons)
Motor neurons
Multipolar
carry impulses from CNS to effectors for action
Afferent nerves
sensory neurons (sensory organs i.e skin-part of the CNS)
Efferent nerves
motor neurons (control muscles i.e contraction muscles-part of the PNS)
Neuroglia
Specialised cells found only in close association with neurons, don’t participate directly in info transfer-there are 4 types of neuroglia
Oligodendrocytes (CNS)
make myelin on many axons (1 olgio=60 axons)
Astrocytes role and function (CNS)
Most abundant type of glia in CNS.
roles are:
1. structural support
2. provides nutrients/neuron homeostasis
3. maintains/regulates synaptic connections
4. reacts to injuries (astrogliosis)
Microglia (CNS)
resident macrophages in brain-“brain immune system”
Increase in phagocytosis after injury causes cells to move to injured area
Ependymal cells (CNS)
provide lining in ventricles (involved in cerebro spinal fluid production)
Shwann Cells
Similar function to oligodentroncytes, but divide more myelinate faster and are more resistant to injury
Satellie cells
similar function to astrocytes, meaning they support neurons and enhance their function
What are action potentials?
electrical signals that propagate along axons, through rapid, transient depolarisation of the cell membrane
What happens in action potential when the neuron is activiated?
When there is a change in the resting membrane potential (RMP) that reaches a certain threshold (-55mV), an action potential will be induced
What happens in depolarisation?
The voltage gated Na+ channels in the neuronal membrane open and sodium flows INTO the cells, bringing +ve electrical charge, increasing membrane potential
What happens in repolarisation?
When the membrane reaches a certain potential of approx 30-40mV, the voltage gated K+ channels open, leading to the exit of potassium ions out of the cell
What happens in hyperpolarisation?
K+ ions continue to leave the neuron, as the voltage gated k+ channels tkae time to close, which causes the membrane potential to drop below the RMP (-70mV), until it reaches around -90mV.
What are the 2 methods of propagating action potentials?
- Continuous propagation (unmyelinated axons)
- Saltatory propagation (myelinated neurons)
What are some of the effects of fibre size on action potential production?
- as fibre sizes increases, conduction velocity of action potentials also increase
- Conduction velocity increases by myelination (saltatoy is faster than continuous propagation in unmyelinated axons)
Synpases
junctions between neurons allowing them to communicate with one another
Describe the function and structure of chemical synapses
unidirectional-most common in mammals
e.g junction between neuron, neuromuscular junction
-have essential components:
1. Pre-synpatic neuron with neurotransmitter housed in pre-synpatic neuron in vesciles
2. Post-synaptic neuron with neurotransmitters beinding sites
3. cleft/gap with enzymes to degrade left over neurotransmitters
Inhibitory post-synaptic potential (IPSP)
Hyperpolarisation of the post synaptic membrane, leading to the inhibition of the post-synaptic neuron
Excitatory post-synaptic potential (ESPS)
Activation of the post-synaptic membrane
Occurs when the effectors of the neurotransmitters on the post-synaptic receptors are excitatory, the binding of the ligand on the receptor leads to the entry of +ve charges in cells, inducing a depolarisation of the post-synaptic membrane
Neurotransmitters
Chemical messengers releases through a membrane through exocytosis and bind to specific receptors at the postsynaptic neuronal membrane.
What are the 3 mechanisms to inactivate neurotransmitters in the synaptic cleft?
- can be broken down by specfic enzymes in the synpatic cleft
- may be reuptake at pre-synaptic button by specific transporter
- Can be diffused away
List and describe the 2 main neurotransmitters in the brain.
- Glutamate
- major excitatory NT in CNS (learning & memory)
- act on metabotropic and ionotropic receptors - GABA (gamma-aminobutyric acid)
- major inhibitory NT in the CNS
- act on GABAergic receptors (ligand gated channel recptors)
What is the Dura Mater?
“hard mother”
external layer of the brain which is thick, though, inelastic
What is the Arachnoid Mater?
thin cell layer with arachnoid trabecullae (web-like collagen projections to pia layer)
What is the Pia Mater?
“tender mother”
internal layer-thin, delicate and tightly covers external contours of brain with blood vessels
What does the Thalamus do?
Site of relay & processing centers
What is the Hypothalamus?
- Highest centre for autonomic control i.e HR, BP, digestion ect
- control & integration centre connected to the limbic system (emotion, behaviour ect) and appetite regulation
- also responsible for hormone regulation
What is the midbrain?
Important for motor control (sleep/awake, attention, temp, auditory & visual information)
What is PONS?
- relays sensory information to cerebellum & thalamus
- contains subconscious somatic and visceral centres
What is the Medulla Oblongata?
Relays information & contains autonomic centers for regulation of visceral function (cardiovascular, respiratory, digestive activities)
What makes up the brain stem
both the midbrain, PONS and medulla oblongata form the brainstem region, which gives rise to the majority of cranial nerves
What is the corpus callosum?
- connects the 2 hemispheres of the brain and is made of mainly nerve fibres
- important for lateralisation (right side= intutive, left side= logical, rational and analytical)
Where is Cerebro Spinal fluid located?
located within 4 ventricles in the brain:
- 2 lateral ventricles (1 in each ventricle)
- 1 in diencephalon
- 1 in brainstem
How is Cerebro Spinal Fluid produced and what are its functions?
-CSF is produced by ependymal cells located in the choroid plexi at the base of the 3rd and 4th ventricles
functions:
1. cushions delicate neural structures
2. Supports brain (oxygen, nutrients)
3. Transports chemical messages, waste products (maintains homeostasis)
What is the cerebral cortex?
A blanket of cells covering the cerebral hemispheres
What are the 4 lobes that form the cerebral cortex?
- Frontal lobe
