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Neurons and the Nervous System

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Presentation on theme: "Neurons and the Nervous System"— Presentation transcript:

1 Neurons and the Nervous System

2 Two Regulatory Systems
Nervous System Fast! Short duration effect Electric (ionic) signals …but also chemicals (neurotransmitters) Affects nearby cells (local) Endocrine System Slower to start Longer duration effect Chemical signals (hormones) Affects any cell (long distance)

3 Nervous and Endocrine are Related
Neurosecretory Cells In brain, but secrete hormones Ex: epinephrine as hormone & neurotransmitter Each system affects outcome of other Ex: suckling…neurons…oxytocin…more milk Ex: chemoreceptors detect glucose in blood…pancreas secretes insulin/glucagon . Feedback Mechanisms Positive: suckling/oxytocin Negative: calcium levels/ PTH/calcitonin

4 Overview of the Vertebrate Nervous System
Divisions of the Nervous System Central Nervous System (CNS) Brain Spinal cord video Peripheral Nervous System (PNS) Nerves

5 Overview of the Vertebrate Nervous System
convey sensory stimulus to the brain “receive” convey motor stimulus to the muscles “act”

6

7 What Does What? 1. Fight or flight 2. Telling skeletal muscle what to do 3. Sending info to CNS 4. Telling glands what to do 5. Rest & digest 6. Telling smooth muscle what to do

8 PNS: Somatic and Autonomic Divisions

9 PNS: Parasympathetic & Sympathetic

10 Reflexes Simplest nerve circuit Adaptive value essential actions
don’t need to think or make decisions about blinking balance pupil dilation startle Purpose: quickly respond to danger Quicker response time • Automatic: no integration with brain signal only goes to spinal cord does not reach brain before response occurs • Fewer neurons / synapses involved in reflex arc shorter distance for signal to travel • Involuntary no conscious control no processing by brain Response is innate (automatic response) rather than learned predetermined neuron pathway (hardwired)

11 The Reflex Arc Components
Stimulus - signal detected by sensory neuron (receptor) Sensory neuron carries message to spinal cord (afferent path) by-passes the brain (shorter path, faster response) U-turn at the interneuron (relay neuron) Motor neuron sends back response (efferent path) Effector – completes response; muscle or gland video

12 Pain withdrawal reflex
Reflex Arc Examples Pain withdrawal reflex Knee jerk reflex

13 The Human Brain Divisions
Cerebrum – “thinking”; conscious actions; all the fancy stuff Cerebellum – coordinates voluntary muscle movements Brainstem – basic life functions (involuntary) Hypothalamus – homeostasis (hunger, thirst, etc)

14 Lateralization of Brain Function
Left hemisphere language, math, logic operations, processing of serial sequences of information, visual & auditory details detailed activities required for motor control Right hemisphere pattern recognition, spatial relationships, non-verbal ideation, emotional processing, parallel processing of information

15 Nervous System Cells Neuron a nerve cell structure fits function
many entry points for signal transmits signal in one direction neuron structure axon

16 Transmission of a Signal
Transmission of signal is like dominoes: start the signal knock down line of dominoes by tipping 1st one (trigger the signal) propagate the signal do dominoes move down the line? no, just a wave through them! re-set the system before you can do it again, have to set up dominoes again (reset the axon) Neuron has similar system protein channels are set up once first one is opened, the rest open in succession all or nothing response “wave” action travels along neuron have to re-set channels so neuron can react again Bozeman video

17 How the Nerve Impulse Travels
Membrane Potential the outside of the cell is more positive the difference in charge while it is not “firing” is called the “resting potential” resting potential video unstimulated neuron = resting potential of -70mV

18 Transmission of a Signal
The Action Potential a momentary reversal in electrical potential across a plasma membrane (as of a neuron or muscle fiber) that occurs when a cell has been activated by a stimulus (a wave that moves down axon of nerve) nerve impulse

19 How the Nerve Impulse Travels
Cells live in a sea of charged ions Anions (negative) more concentrated within the cell Cl-, charged amino acids (aa-) Cations (positive) more concentrated in the extracellular fluid Na+

20 How the Nerve Impulse Travels Propagation of the Action Potential
Resting Potential Cells have voltage: voltage gated ion channels (opposite charges on opposite sides of cell membrane) Membrane is polarized negative inside; positive outside charge gradient present stored energy (like a battery) animation

21 Propagation of the Action Potential
2. Depolarization Stimulus: causes Na+ channels to open Na+ ions diffuse into cell Once enough Na+ moves in, membrane is “depolarized” charges reverse at that physical point on axon positive inside; negative outside

22 Propagation of the Action Potential
Action potential: nerve impulse “wave” that travels down neuron brain  finger tips in milliseconds change in charge opens next Na+ gates down the line “voltage-gated” channels Na+ ions continue to diffuse into cell

23 Propagation of the Action Potential
Charges re-set as action potential continues down neuron K+ channels open K+ channels open up more slowly than Na+ channels K+ ions diffuse out of cell charges reverse back at that physical point on axon negative inside; positive outside

24 Propagation of the Action Potential
Combined waves travel down neuron wave of opening ion channels moves down neuron signal moves in one direction     flow of K+ out of cell stops activation of Na+ channels in wrong direction

25 Propagation of the Action Potential
Action potential propagates Ion channels open & close in response to changes in charge across membrane

26 Propagation of the Action Potential
Repolarization After firing a neuron has to re-set itself Na+ needs to move back out K+ needs to move back in both are moving against concentration gradients a pump is needed

27 How the Nerve Re-sets Itself
Sodium Potassium Pump Active transport protein in membrane requires ATP 3 Na+ pumped out 2 K+ pumped in Re-sets charge across membrane Na-K pump maintains this difference

28 How the Nerve Re-sets Itself
4. Resting potential re-established: neuron is ready to fire again

29 Action Potential Graph
1. Resting potential 2. Stimulus reaches threshold potential 3. Depolarization Na+ channels open; K+ channels closed 4. Na+ channels close; K+ channels open 5. Re-polarization reset charge gradient 6. Undershoot K+ channels close slowly

30 Action Potential Graph

31 Saltatory Conduction Action potentials can only be generated at nodes of Ranvier axon coated with Schwann cells covered by myelin sheath (fatty covering) insulates axon found on most large sensory nerves Action potentials jump from node to node increasing conduction of impulse Multiple Sclerosis- immune system (T cells) attack myelin sheath- causes loss of signal 150 m/sec vs. 5 m/sec (330 mph vs. 11 mph) video

32 Propagation of Impulse to Other Nerves
animation – chemical synapse Bozeman video Chemical Synapse: junction between neurons that allows transmission of signals between neurons Events at synapse: action potential depolarizes membrane - opens Ca++ channels neurotransmitter vesicles fuse with membrane - release neurotransmitter to synapse (diffusion) neurotransmitter binds with protein receptor ion-gated channels open neurotransmitter degraded or reabsorbed presynaptic neuron postsynaptic neuron CLEFT

33 Nerve Impulse in Next Neuron
Each Neuron makes connections with many other neurons Post-synaptic neuron triggers nerve impulse in next nerve cell chemical signal opens ion-gated channels Na+ diffuses into cell K+ diffuses out of cell process starts over again

34 Neurotransmitters Chemical messengers more than 40 identified
transmit signals across a chemical synapse, from one neuron to another "target" neuron Released from synaptic vesicles in synapses into the synaptic cleft received by receptors on the target cells.

35 Neurotransmitters Acetylcholine
transmit signal to skeletal muscle Epinephrine (adrenaline) & Norepinephrine fight-or-flight response Dopamine widespread in brain affects sleep, mood, attention & learning lack of dopamine in brain associated with Parkinson’s disease excessive dopamine linked to schizophrenia Serotonin

36 Neurotransmitters Weak point of nervous system
any substance that affects neurotransmitters or mimics them affects nerve function gases: nitrous oxide, carbon monoxide mood altering drugs depressants quaaludes, barbiturates stimulants amphetamines, caffeine, nicotine hallucinogenic drugs: LSD, peyote SSRIs: Prozac, Zoloft, Paxil neurotoxin poisons acetylcholinesterase: breaks down acetylcholine snake venom, sarin, insecticides

37 Neurological Disorder

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