Rucete ✏ Biology In a Nutshell
1. Structure of a Neuron
- Cell Body: contains nucleus and organelles
- Dendrites: receive incoming signals
- Axon: transmits impulses away from the cell body
- Flow of impulse: dendrite → cell body → axon → axon terminals
2. Types of Neurons
- Sensory Neurons (Afferent): transmit signals from receptors to the CNS
- Motor Neurons (Efferent): transmit signals from CNS to effectors (muscles or glands)
- Interneurons (Association Neurons): connect sensory and motor neurons within the CNS
3. Nerve Impulse Transmission (Along a Neuron)
a) Resting Potential
- Neuron is polarized at about -70 mV
b) Action Potential
- Triggered when stimulus reaches threshold
- Na⁺ channels open, Na⁺ enters → depolarization
- Then K⁺ channels open, K⁺ exits → repolarization
- Hyperpolarization may occur (~ -80 mV)
c) Refractory Period
- Time when the neuron cannot respond to a new stimulus
- Na⁺ and K⁺ return to original positions
4. Transmission Across a Synapse
- Involves presynaptic neuron, synapse, and postsynaptic cell
- Neurotransmitter is released into synaptic cleft and binds to receptors
a) Excitatory Postsynaptic Potential (EPSP)
- Makes the neuron more likely to fire
b) Inhibitory Postsynaptic Potential (IPSP)
- Makes the neuron less likely to fire
5. Common Neurotransmitters
- Acetylcholine: stimulates skeletal muscle
- Epinephrine, Norepinephrine, Dopamine, Serotonin: mood and alertness
- GABA: main inhibitory neurotransmitter in the CNS
6. Divisions of the Nervous System
a) Central Nervous System (CNS)
- Includes the brain and spinal cord
b) Peripheral Nervous System (PNS)
- Sensory Neurons: from body to CNS
- Motor Neurons: from CNS to effectors
i) Somatic Nervous System
- Controls voluntary movements via skeletal muscles
ii) Autonomic Nervous System
- Controls involuntary functions (e.g., digestion, heartbeat)
▸ Sympathetic Nervous System
- Fight or flight response
▸ Parasympathetic Nervous System
- Rest and digest response
7. Reflex Arc
- Direct pathway: sensory neuron → interneuron → motor neuron
- Enables fast, involuntary responses without brain involvement
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Biology in a nutshell