MNB 14 WT 2024-25 PDF - RCSI

Musculoskeletal System, Nervous System & Bioelectricity MNB.14 Peripheral nervous system and reflexes P r o f Wa r r e n T h o m a s DAT E: 26 No v 2 0 2 4 Learning outcomes At the end of this lecture, the learner will be able to Describe the effects of neurotransmitters on various syst...

Musculoskeletal System, Nervous System & Bioelectricity MNB.14 Peripheral nervous system and reflexes P r o f Wa r r e n T h o m a s DAT E: 26 No v 2 0 2 4 Learning outcomes At the end of this lecture, the learner will be able to Describe the effects of neurotransmitters on various systems in the body. Recall the peripheral nervous system. Describe the structure of the spinal cord including its connection to the somatic nervous system. Outline the operation of the reflex arc. Differentiate between monosynaptic and polysynaptic reflexes. MN B.14 Peri pheral nervous system and refl exes 2 Chemical synapse Sequence of events leading to the conversion of electrical energy (action potential) to chemical signal (neurotransmitter), and back to electrical signal (action potential). In the ANS, this can either be neuron-neuron (i.e. at ganglia) or neuron-target tissue MN B.14 Peri pheral nervous system and refl exes 3  Neurotransmitters About 40 different chemicals are known to act as neurotransmitters. Each type of neuron is thought to release only one small-molecule type of neurotransmitter. However, the neuron may release one or more neuropeptides at the same time. A postsynaptic neuron may have receptors for a number of neurotransmitters These may be both excitatory and inhibitory. http://www.differencebetween.com/difference-between- neuropeptides-and-vs-neurotransmitters/ MN B.14 Peri pheral nervous system and refl exes 4 Neurotransmitters Transmitter Abbrev Location Receptor Effect Acetylcholine ACh NMJ, Parasympathetic NS, Nicotinic, Excitatory ANS ganglia, Brain Muscarinic Noradrenaline NA; Adr Sympathetic NS, brainstem, Alpha (a) Excitatory (Norepinephrine) hypothalamus Beta (b) Dopamine DA Cerebral cortex, basal D1 – D5 Inhibitory ganglia, spinal cord, enteric NS, hypothalamus Serotonin 5-HT Cerebellum, hypothalamus, 5-HT1 – 5-HT7 Excitatory/inhibitory spinal cord, enteric NS -aminobutyric acid GABA Cerebral cortex, cerebellum, GABAA Inhibitory spinal cord GABAB MN B.14 Peri pheral nervous system and refl exes 5 Peripheral nervous system (PNS) PNS Autonomic Nervous System Somatic Nervous System (ANS) Sympathetic Parasympathetic Enteric MN B.14 Peri pheral nervous system and refl exes 6 Peripheral nervous system (PNS) 31 pairs of spinal nerves exit between vertebrae Spinal nerves: Cervical –neck region (C1-C8) Thoracic –Chest region (T1-T12) Lumbar -Lower back (L1-L5) Sacral –Base of spine (S1-S5) MN B.14 Peri pheral nervous system and refl exes 7 Autonomic nervous system Target Two nerves from the spinal cord: Pre-ganglionic neuron Runs from the spinal cord to the ganglion Synapse First nerve synapses with second nerve Post-ganglionic neuron Runs from the ganglion to the organ MN B.14 Peri pheral nervous system and refl exes 8 Sympathetic nervous system Paravertebral ganglia Thoracolumbar outflow Short pre-synaptic (ganglionic) neuron Long post-synaptic neuron Connect to 2 chains of ganglia –Paravertebral ganglia (left and right sides) MN B.14 Peri pheral nervous system and refl exes 9  Sympathetic nervous system Paravertebral ganglia Runs from base of the skull to coccyx 2 paravertebral ganglia 15-16 ganglia per column Allows distribution of nerves to organs and glands MN B.14 Peri pheral nervous system and refl exes 10 Sympathetic nervous system MN B.14 Peri pheral nervous system and refl exes 11 Sympathetic nervous system Structure Sensory neurons enter by the dorsal root Afferent neurons SNS neurons leave the ventral root Efferent neurons MN B.14 Peri pheral nervous system and refl exes 12  Sympathetic nervous system Outcomes: 1. Pass through horn (white ramus) 2. Travel up the ganglion (Superior) or travel down ganglion (Inferior) 3. Synapse in the ganglion 4. Synapse in an abdominal ganglion MN B.14 Peri pheral nervous system and refl exes 13 Sympathetic nervous system Neurotransmitters of the SNS Synapses in the ganglia Where the preganglionic neuron reaches the post-ganglionic neuron Transmitter is Acetylcholine (ACh) Post-ganglionic neuron terminal At the organ Transmitter is Adrenaline MN B.14 Peri pheral nervous system and refl exes 14 Sympathetic nervous system Effects: Pupil dilation Bronchial relaxation Increase in heart rate Stimulates glucose release Adrenaline release MN B.14 Peri pheral nervous system and refl exes 15  Parasympathetic Nervous System “Rest and digest” Craniosacral outflow Preganglionic neurons originate from the cranial nerves III, VII, IX and X and sacral spinal nerves S2-S4. Vagus nerve (X) carries nearly 80% of the total craniosacral flow. Long preganglionic neuron. Ganglion lies close to the target organ. Short post-ganglionic neuron. Sympathetic and Parasympathetic systems are antagonistic. MN B.14 Peri pheral nervous system and refl exes 16 Parasympathetic nervous system No paravertebral ganglia (sympathetic chain) like in the SNS The pre-ganglionic neuron releases ACh. The postganaglionic neuron also releases ACh. MN B.14 Peri pheral nervous system and refl exes 17 Synaptic transmission ACh is broken down by an enzyme called Acetylcholinesterase (AChE). The degradation products are taken into the pre-synapse where it is re-made into ACh and stored in vesicles. MN B.14 Peri pheral nervous system and refl exes 18 Spinal Cord Essentially the spinal cord has two functions: – Transmits nerve impulses to and from the Brain. – Acts as a Reflex Centre. It is protected by the neural arches of the vertebrae and lies in the vertebral canal. Histology Divided into two areas: Grey matter Contains the somata and dendrites of the motor and connector neurons (interneurons) Neuroglial cells Blood vessels White matter Bundles of axons and dendrites MN B.14 Peri pheral nervous system and refl exes 19 Spinal reflexes Reflex actions have a relatively fixed reaction pattern to a simple stimulus. The response is predictable and automatic and does not require conscious thought. Many activities in the body are regulated by reflex actions. The individual components of the reflex process form a Reflex arc. MN B.14 Peri pheral nervous system and refl exes 20 Reflex arc In general, sensory stimuli are picked up by receptor cells and carried toward the spinal cord in long afferent somatic nerve fibres. MN B.14 Peri pheral nervous system and refl exes 21 Reflex arc After the craniospinal ganglion (Dorsal Root Ganglion) the impulse continues via the axon to the spinal cord. MN B.14 Peri pheral nervous system and refl exes 22  Reflex arc In the Grey Matter it synapses with interneurons MN B.14 Peri pheral nervous system and refl exes 23 Reflex arc The interneuron relays the stimulus to the efferent neuron MN B.14 Peri pheral nervous system and refl exes 24  Reflex arc Depending on the reflex arc, one or more efferent neurons are stimulated. The signal leaves the spinal cord through the ventral root for the effector organ MN B.14 Peri pheral nervous system and refl exes 25  Reflex arc Stimulation of the effector organ(s) by their motor neurons produces the desired reflex reaction. MN B.14 Peri pheral nervous system and refl exes 26 Monosynaptic vs polysynaptic reflexes When a reflex arc consists of only two neurons in an animal (one sensory neuron, and one motor neuron), it is defined as monosynaptic. – Monosynaptic refers to the presence of a single chemical synapse. – In the case of peripheral muscle reflexes (patellar reflex), brief stimulation to the muscle spindle results in contraction of the agonist or effector muscle. Polysynaptic reflex pathways, one or more interneurons connect afferent (sensory) and efferent (motor) signals. All but the most simple reflexes are polysynaptic, allowing processing or inhibition of polysynaptic reflexes within the brain. MN B.14 Peri pheral nervous system and refl exes 27 Stretch reflex / Patella tap To brain A feedback mechanism that Stretching stimulates 2 SENSORY 1 SENSORY RECEPTOR NEURON causes contraction of a skeletal (muscle spindle) excited + muscle in response to stretching of the same muscle – this reflex 5 EFFECTOR + – helps avoid injury by preventing (same muscle) contracts and overstretching (lengthening) of a relieves the Spinal Nerve stretching muscle. + 4 MOTOR Inhibitory NEURON interneuron excited 3 Within INTEGRATING This is an example of a CENTER (spinal cord), sensory neuron activates monosynaptic reflex. motor neuron Antagonistic Motor neuron to muscles relax antagonistic muscles is inhibited MN B.14 Peri pheral nervous system and refl exes 28  To brain To brain Tendon reflex Inhibitory Inhibitory interneuron interneuron 4 MOTOR MOTOR NEURON NEURON 5 EFFECTOR inhibited inhibited (muscle attached ++ to same tendon) 2 SENSORY SENSORY ++ ++ relaxes and NEURON NEURON excited excited A feedback mechanism to relieves excess tension Increased tension Increased tension –– cause muscle relaxation when stimulates stimulates 1 SENSORY SENSORY ++ muscle tension is too great RECEPTOR (tendon) RECEPTOR (tendon) (and ruptures the tendon). Spinal Spinal nerve nerve 3 Within Within INTEGRATING INTEGRATING Excitatory Excitatory It is less sensitive than the CENTER (spinal CENTER (spinal cord), cord), interneuron interneuron ++ sensory neuron sensory neuron activates activates stretch reflex, but it can inhibitory interneuron inhibitory interneuron override the stretch reflex when tension is too great, making Antagonistic Antagonistic muscles muscles you drop a very heavy weight. contract contract Motor neuron Motor neuron to to antagonistic antagonistic muscles is muscles is excited excited This is an example of a polysynaptic reflex.  Solomon Chapter 41 and 42 Chiras. Human Biology. Chapter 10. Learning Resources MN B.1 4 Peri p he ra l ne rvo us syste m a nd re fl e xes 30 Thank you F O R M O R E I N F O R M AT I O N P L E A S E C O N TA N T P rof War ren Tho ma s E MA IL:w ath omas@rc si-mub.c om 31