Introduction to brain anatomy Flashcards
What is the 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 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 for Parasympathetic Nerves?
Parasympathetic Nerves
- Cranial nerves: constrict pupils, stimulate saliva, slow heartbeat, constrict airways, inhibit release of glucose, stimulate gallbladder
- Sacral nerves: contract bladder, promote erection of genitals
What are the components of the autonomic nervous system for Sympathetic Nerves?
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?
There normally 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 us alive on a minute-to-minute basis
What are the components of the brainstem?
Midbrain and hindbrain
