Introduction to brain anatomy Flashcards
What is the phenomenon of convergence?
When many pre-synaptic neurons converge on a single post-synaptic neuron
- average neuron receives 10,000 different inputs from synapses on it
- > a single cell receives multiple signals
What is the phenomenon of divergence?
Ability of a single cell to project on multiple cells
- axons of most pre-synpatic neurons divide into many branches that diverge to end on many post-synaptic neurons
- approx. 1,000 different axon terminals from one single neuron
- > a single cell sends multiple signals
What is the result of convergence and divergence?
Neural networks
- there are multiple ways of getting from one cell to another
- different cells will be excited according to the route chosen
- > different neural consequences
What is the general organisation of the Nervous System?
Central Nervous System (CNS)
> Brain
> Spinal Cord
Peripheral Nervous System (PNS) > Somatic (which we are conscious of) - Sensory - Motor > Autonomic (which we are not aware of) - Parasympathetic - Sympathetic
What are the components of the autonomic nervous system?
Parasympathetic Nerves > Cranial nerves - constrict pupils - stimulate saliva - slow heartbeat - constrict airways - inhibit release of glucose ; stimulate gallbladder > Sacral nerves - contract blader - promote erection of genitals
Sympathetic nerves > Thoracic nerves - dilate pupils - inhibit salivation - increase heartbeat - relax airways - stimulate release of glucose ; inhibit gallbladder - secrete epinephrine and norepinephrine > Lumbar nerves - relax bladder - promote ejaculation and vaginal contraction
How do the parasympathetic and sympathetic nervous systems work?
> They work in opposite ways
- e.g. PaNS constricts pupils vs. SyNS dilates pupils
> Although they send peripheral branches, they’re not restricted to the periphery alone
- in the brain, there are pathways wholly concerned with parasympathetic and sympathetic function
How do you differentiate neurons from the CNS and the PNS?
- If a neuron is entirely contained within the brain and/or spinal cord -> CNS neuron
- If any part of a neuron (dendrites, axon or cell body) projects outside of these structures -> PNS neuron
What are the anatomical compartments of the CNS?
> Forebrain
> Midbrain
> Hindbrain
- Pons
- Cerebellum
- Medulla
> Spinal cord
Why are spinal nerves “mixed” nerves?
They are composed of: > Receptors > Sensory neurons (dorsal input) - dorsal root ganglia -> dorsal root > Interneuron > Motor neuron (ventral output) > Muscle (receives information)
What are the divisions of spinal nerves?
Through which component do these nerves leave the spinal canal?
31 spinal nerves
- Cervical nerves (C1 -> C8)
- Thoracic nerves (T1 -> T12)
- Lumbar nerves (L1 -> L5)
- Sacral nerves (S1 -> S5)
- Coccygeal nerve (1)
All leave through intervertebral foramen
Where does the spinal cord end? What happens consequently?
Spinal cord ends at vertebral L1-L2 (lumbar division)
- > any nerve below L1 and L2 has to travel down until it finds its corresponding intervertebral foramen and exits
- > Cauda equina (horse’s tail): a group of nerves (S1 to Coccygeal nerve) at the base of spinal cord where there’s neural tissue (cell bodies) involved
Why is the cauda equina clinically important?
A needle can be inserted below L1 and L2 - e.g. to drain cerebral spinal fluid diagnostically, or if there’s a build up pressure - knowing you’re going below the spinal cord itself and therefore won’t damage it
e.g. lumbar punctures
What is the medulla and what is its function?
> Medulla is the oldest part of the hindbrain
Oldest part of the brain
Controls life-supporting centres
-> keeps you alive on a minute-to-minute basis
What are the components of the brainstem?
Midbrain and hindbrain
What is the role of the midbrain?
Relays information between the forebrain (above) and the hindbrain (below).
